feat: Add Prometheus labels and annotations to role-group services

[siegfriedweber]

Description

Add Prometheus labels and annotations to role-group services

• The following labels and annotations are added to the role-group services:

  metadata:
    labels:
      prometheus.io/scrape: "true"
    annotations:
      prometheus.io/path: /_prometheus/metrics
      prometheus.io/port: "9200"
      prometheus.io/scheme: https
      prometheus.io/scrape: "true"

• The metrics are tested in an integration test with a Prometheus ServiceMonitor.
• The metrics feature is documented.

Part of #19

Documentation

https://docs.stackable.tech/home/nightly/opensearch/usage-guide/monitoring/

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Author

• Changes are OpenShift compatible
• Helm chart can be installed and deployed operator works
• Integration tests passed (for non trivial changes)
• Links to generated (nightly) docs added

Reviewer

• Code contains useful comments
• Code contains useful logging statements
• (Integration-)Test cases added
• Documentation added or updated. Follows the style guide.
• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added
• Links to generated (nightly) docs added
• Release note snippet added
• Add type/deprecation label & add to the deprecation schedule
• Add type/experimental label & add to the experimental features tracker

[razvan]

LGTM!

--- PASS: kuttl (105.34s)
    --- PASS: kuttl/harness (0.00s)
        --- PASS: kuttl/harness/metrics_opensearch-3.1.0_openshift-false_opensearch_home-_stackable_opensearch (105.32s)
PASS