K8s naming convention rational and additional documentation

[jinja2]

Fixes #2245

Changes

Adds rationale and further guidance for naming Kubernetes resources.

Merge requirement checklist

• [ x] CONTRIBUTING.md guidelines followed.
• [ x] Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• [ ] schema-next.yaml updated with changes to existing conventions.