Add draft error doc

refs #17235
Add error doc to planning tree
Change tests from "updated" to "modified"
Change "updated" to "modified"
Convert vendor details to use serializer
Update vendor serialization logic, update tests for updated times
Merge branch 'enhancement/17337' of github.com:osu-cass/whats-fresh-api into enhancement/17337

Conflicts:
	whats_fresh/whats_fresh_api/views/serializer.py
Fix extraneous comma