Support monitoring Envoy with Prometheus Operator

What does this MR do?

Add ServiceMonitor and PodMonitor for Envoy

• Support ServiceMonitor for Envoy Gateway.
• Support PodMonitor for Envoy Proxy. Uses Pod Monitor because (LoadBalancer) Service does not expose metrics port.

Closes #6273 (closed)

Changelog: added

Related issues

Test Plan

1. Install Prometheus Operator: https://prometheus-operator.dev/docs/getting-started/installation/

2. Depending on your install method you might need to setup a Prometheus CR

3. Install GitLab chart and enable the Envoy Pod and ServiceMonitor

4. Confirm Prometheus scraped Envoy Gateway and Proxy. This can be done by port forwarding port 9090 to the managed Prometheus Pod/Service.

   

Author checklist

For general guidance, please follow our Contributing guide.

Required

For anything in this list which will not be completed, please provide a reason in the MR discussion.

• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated.
• Tests added/updated, and test plan for scenarios not covered by automated tests.
• Equivalent MR/issue for omnibus-gitlab opened.

Reviewers checklist

• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab chart.