chore: ensure metrics are correctly exposed

[maltesander]

Description

Part of stackabletech/issues#747
This PR adds Prometheus annotations and adds a pod port for metrics

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
• CRD changes approved
• CRD documentation for all fields, following the style guide.
• Helm chart can be installed and deployed operator works
• Integration tests passed (for non trivial changes)
• Changes need to be "offline" compatible
• Links to generated (nightly) docs added
• Release note snippet 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

[adwk67]

LGTM

[lfrancke]

Please add a release note snippet. This could be considered a bug or a new feature. So you can use the form "Previously, this went wrong. With this release, this was fixed in the following way." but you don't have to.

[maltesander]

Release snippet:

Previously, the airflow-operator did not expose Prometheus annotations containing the http(s) scheme or the metrics path and port. This was added in this PR and allows custom relabel configs in Prometheus using these annotations.