Removing default prometheus service annotations in Helm

[airamare01]

Checklist

• Follow the manual testing process
• Update changelog
• Update Kubernetes update doc

Test plan

Tested locally. In a nutshell:

This modification:

1. Removes the Prometheus scrape annotations entirely.
2. Keeps the ability to add custom service annotations through .Values.executor.serviceAnnotations.
3. Only includes the annotations section if there are actually any custom annotations to add.
4. This approach allows removal of the potentially problematic Prometheus scrape targets while maintaining flexibility for users to add their own custom annotations if needed.
5. Keeps the YAML clean by not including an empty annotations section when it's not needed.

[airamare01]

Duplicate issue here: #529

[loujar]

It looks like the Executor Prometheus scrape annotations are still present in this PR:

metadata:
  annotations:
    prometheus.io/port: "6060"
    sourcegraph.prometheus/scrape: "true"

[airamare01]

Fixed it @loujar