Use service in discovery configmap

[maltesander]

Description

• Use metastore service instead of single pod references in discovery config map to enable HA

fixes #380

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

Preview Give feedback

1. Changes are OpenShift compatible
2. CRD changes approved
3. Helm chart can be installed and deployed operator works
4. Integration tests passed (for non trivial changes)
5. Changes need to be "offline" compatible

Reviewer

Preview Give feedback

1. Code contains useful comments
2. (Integration-)Test cases added
3. Documentation added or updated
4. Changelog updated
5. Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

Preview Give feedback

1. Feature Tracker has been updated
2. Proper release label has been added

[adwk67]

Just some typos. Docs are consistent and draw distinction between derby/postgres usage re. replicas. However, although multiple replicas are now reachable internally via a service, the nodeport configmap points to each pod individually which means an external service will still have to some manual work itself to provide HA.

[adwk67]

Having discussed this today - LGTM! Maybe we need a specific test for this, but I'll leave that up to you.