docs: ADR for adding event bus kafka cookiecutter

[jesperhodge]

Merge checklist: Check off if complete or not applicable:

• [ ] Changelog record added
• [ ] Documentation updated (not only docstrings)
• [ ] Fixup commits are squashed away
• [ ] Unit tests added/updated
• [ ] Manual testing instructions provided
• [ ] Noted any: Concerns, dependencies, deadlines, tickets