[kube-state-metrics] fix: do not render *Probe.httpGet.httpHeaders when array is empty

[MadJlzz]

What this PR does / why we need it

This PR is fixing invalid YAML rendering when any probes httpHeaders are unset. It's not mandatory because YAML spec treats undefined values as null but some linters flag those as "errors".

Which issue this PR fixes

I can open an issue for traceability, I just decided not to do it - please tell me if you want me to.

• fixes #

Special notes for your reviewer

Before:

startupProbe:
  failureThreshold: 3
  httpGet:
    httpHeaders:
    path: /healthz
    port: http
    scheme: HTTP
[...]
livenessProbe:
  failureThreshold: 3
  httpGet:
    httpHeaders:
    path: /livez
    port: http
    scheme: HTTP
[...]
readinessProbe:
  failureThreshold: 3
  httpGet:
    httpHeaders:
    path: /readyz
    port: metrics
    scheme: HTTP

After:

startupProbe:
  failureThreshold: 3
  httpGet:
    path: /healthz
    port: http
    scheme: HTTP
[...]
readinessProbe:
  failureThreshold: 3
  httpGet:
    path: /readyz
    port: metrics
    scheme: HTTP
[...]
livenessProbe:
  failureThreshold: 3
  httpGet:
    path: /livez
    port: http
    scheme: HTTP

Checklist

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [prometheus-couchdb-exporter])