[prometheus-blackbox-exporter] make ServiceMonitor apiVersion configurable

[firasmosbehi]

Summary

This PR adds a configurable ServiceMonitor API version for prometheus-blackbox-exporter and addresses #6086.

Problem

Some managed Kubernetes providers expose ServiceMonitor CRDs under provider-specific API groups (for example azmonitoring.coreos.com/v1). The chart currently hardcodes monitoring.coreos.com/v1, which prevents native deployment of ServiceMonitor resources in those environments.

Root cause

Both ServiceMonitor templates (servicemonitor.yaml and selfservicemonitor.yaml) hardcode apiVersion: monitoring.coreos.com/v1.

Fix

• Added serviceMonitor.apiVersion to values with default monitoring.coreos.com/v1.
• Updated both ServiceMonitor templates to use this value.
• Bumped chart version from 11.8.0 to 11.8.1.

Validation

• helm lint charts/prometheus-blackbox-exporter
• helm template test charts/prometheus-blackbox-exporter --set serviceMonitor.enabled=true --set serviceMonitor.selfMonitor.enabled=true --set serviceMonitor.apiVersion=azmonitoring.coreos.com/v1 ...
• Verified both rendered ServiceMonitor manifests use apiVersion: azmonitoring.coreos.com/v1.

Compatibility

Default behavior is unchanged because the new value defaults to monitoring.coreos.com/v1.