feat: improve error message, if traffic is blocked by network policy

[lukasmetzner]

If the connection to the Hetzner API is blocked by a NetworkPolicy the user receives an error message, which should be improved:

cert-manager-webhook-hetzner-759cb46c65-b4qnh time=2025-11-20T12:48:02.369Z level=INFO source=/home/runner/work/cert-manager-webhook-hetzner/cert-manager-webhook-hetzner/internal/hetzner/solver.go:87 msg="creating DNS TXT record" zone-name=example.com zone-rrset-name=_acme-challenge                                                                                                                                                                                                                                                                               
cert-manager-webhook-hetzner-759cb46c65-b4qnh time=2025-11-20T12:48:36.405Z level=INFO source=/home/runner/work/cert-manager-webhook-hetzner/cert-manager-webhook-hetzner/internal/hetzner/solver.go:87 msg="creating DNS TXT record" zone-name=example.com zone-rrset-name=_acme-challenge                                                                                                                                                                                                                                                                               
cert-manager-webhook-hetzner-759cb46c65-b4qnh time=2025-11-20T12:49:10.422Z level=INFO source=/home/runner/work/cert-manager-webhook-hetzner/cert-manager-webhook-hetzner/internal/hetzner/solver.go:87 msg="creating DNS TXT record" zone-name=example.com zone-rrset-name=_acme-challenge                                                                                                                                                                                                                                                                               cert-manager-webhook-hetzner-759cb46c65-b4qnh time=2025-11-20T12:49:44.433Z level=INFO source=/home/runner/work/cert-manager-webhook-hetzner/cert-manager-webhook-hetzner/internal/hetzner/solver.go:87 msg="creating DNS TXT record" zone-name=example.com zone-rrset-name=_acme-challenge                                                                                                                                                                                                                                                                               cert-manager-webhook-hetzner-759cb46c65-b4qnh time=2025-11-20T12:50:18.444Z level=INFO source=/home/runner/work/cert-manager-webhook-hetzner/cert-manager-webhook-hetzner/internal/hetzner/solver.go:87 msg="creating DNS TXT record" zone-name=example.com zone-rrset-name=_acme-challenge                                                                                                                                                                                                                                                                               cert-manager-webhook-hetzner-759cb46c65-b4qnh time=2025-11-20T12:50:58.444Z level=INFO source=/home/runner/work/cert-manager-webhook-hetzner/cert-manager-webhook-hetzner/internal/hetzner/solver.go:87 msg="creating DNS TXT record" zone-name=example.com zone-rrset-name=_acme-challenge                                                                                                                                                                                                                                                                               cert-manager-webhook-hetzner-759cb46c65-b4qnh E1120 12:51:19.207498       1 finisher.go:175] "Unhandled Error" err="FinishRequest: post-timeout activity - time-elapsed: 2m42.839957537s, panicked: false, err: <nil>, panic-reason: <nil>" logger="UnhandledError"                   
cert-manager-webhook-hetzner-759cb46c65-b4qnh E1120 12:51:47.839371       1 finisher.go:175] "Unhandled Error" err="FinishRequest: post-timeout activity - time-elapsed: 2m37.435480345s, panicked: false, err: <nil>, panic-reason: <nil>" logger="UnhandledError"                   
cert-manager-webhook-hetzner-759cb46c65-b4qnh E1120 12:52:29.346688       1 finisher.go:175] "Unhandled Error" err="FinishRequest: post-timeout activity - time-elapsed: 2m44.925749132s, panicked: false, err: <nil>, panic-reason: <nil>" logger="UnhandledError"                   
cert-manager-webhook-hetzner-759cb46c65-b4qnh E1120 12:53:01.182528       1 finisher.go:175] "Unhandled Error" err="FinishRequest: post-timeout activity - time-elapsed: 2m42.750792382s, panicked: false, err: <nil>, panic-reason: <nil>" logger="UnhandledError"                   
cert-manager-webhook-hetzner-759cb46c65-b4qnh E1120 12:53:29.312075       1 finisher.go:175] "Unhandled Error" err="FinishRequest: post-timeout activity - time-elapsed: 2m36.869929322s, panicked: false, err: <nil>, panic-reason: <nil>" logger="UnhandledError"                   
cert-manager-webhook-hetzner-759cb46c65-b4qnh time=2025-11-20T12:54:12.464Z level=INFO source=/home/runner/work/cert-manager-webhook-hetzner/cert-manager-webhook-hetzner/internal/hetzner/solver.go:87 msg="creating DNS TXT record" zone-name=example.com zone-rrset-name=_acme-challenge                                                                                                                                                                                                                                                                               cert-manager-webhook-hetzner-759cb46c65-b4qnh E1120 12:54:13.730942       1 finisher.go:175] "Unhandled Error" err="FinishRequest: post-timeout activity - time-elapsed: 2m41.28798896s, panicked: false, err: <nil>, panic-reason: <nil>" logger="UnhandledError"                    
cert-manager-webhook-hetzner-759cb46c65-b4qnh E1120 12:57:30.077963       1 finisher.go:175] "Unhandled Error" err="FinishRequest: post-timeout activity - time-elapsed: 2m43.615811779s, panicked: false, err: <nil>, panic-reason: <nil>" logger="UnhandledError"                   
cert-manager-webhook-hetzner-759cb46c65-b4qnh time=2025-11-20T13:00:06.487Z level=INFO source=/home/runner/work/cert-manager-webhook-hetzner/cert-manager-webhook-hetzner/internal/hetzner/solver.go:87 msg="creating DNS TXT record" zone-name=example.com zone-rrset-name=_acme-challenge                                                                                                                                                                                                                                                                               cert-manager-webhook-hetzner-759cb46c65-b4qnh E1120 13:03:19.300791       1 finisher.go:175] "Unhandled Error" err="FinishRequest: post-timeout activity - time-elapsed: 2m38.815038864s, panicked: false, err: <nil>, panic-reason: <nil>" logger="UnhandledError"

This should also be reproducible using mitmproxy.