WIP
convert existing histories to content type
fix flake error
after review
after review
updated changelog
after quamilek review
after review
added history documentation
changed history doc
small changes
added migration
Merge pull request #434 from ar4s/feature/177-history-on-content-type

History on content type
Merge branch 'develop' into 429-WIP-assigned-count

Conflicts:
	src/ralph_assets/models_assets.py
	src/ralph_assets/models_sam.py