Send WebSub events for object updates

[Floppy]

Resolves #4097

This is a WIP for websub support. When objects are created or updated, they will send a ping to a websub hub if set.

This is basically tested and working, but I still need to:

• add tests and get decent coverage
• work out how to notify about new item (topics)
• add events for other objects: creators, collections, and probably users

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ -0.03% (target: -1.00%)	✅ 77.78%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (3028a9a)	3837	3246	84.60%
Head commit (ddfbc5e)	3855 (+18)	3260 (+14)	84.57% (-0.03%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#4099)	18	14	77.78%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[coderofsalvation]

oh this is awesome progress!
I'm not sorry for NERD-SNIPING you with this topic :)