[prometheus-fastly-exporter] add podLabels support

[firasmosbehi]

Summary

This PR implements support for custom pod labels in the prometheus-fastly-exporter chart and addresses #6709.

Problem

The chart exposed pod annotations but did not expose pod labels for the Deployment pod template. Users running GitOps workflows (for example Argo CD) could not reliably inject required standard pod labels without forking or post-render patching.

Root cause

templates/deployment.yaml only rendered selector labels under spec.template.metadata.labels, and values.yaml did not define a podLabels value.

Fix

• Added podLabels in chart values with an empty-map default.
• Updated Deployment pod template labels to merge podLabels when provided.
• Bumped chart version from 0.11.0 to 0.11.1.

Validation

• helm lint charts/prometheus-fastly-exporter
• helm template test charts/prometheus-fastly-exporter --set podLabels.team=platform and verified rendered team: platform label in pod template metadata.

Notes

This change is backward compatible because podLabels defaults to {} and existing label behavior is preserved when unset.