feat: add RDBMS support to 8.9 helm charts

[stoerti]

Which problem does the PR fix?

Adds RDBMS configuration support to the Camunda platform charts

What's in this PR?

Checklist

Please make sure to follow our Contributing Guide.

Before opening the PR:

• In the repo's root dir, run make go.update-golden-only.
• There is no other open pull request for the same update/change.
• Tests for charts are added (if needed).
• In-repo documentation are updated (if needed).

After opening the PR:

• Did you sign our CLA (Contributor License Agreement)? It will show once you open the PR.
• Did all checks/tests pass in the PR?