Added specific handling to show relevant error message when user
creation fails due to invite sending errors, while also returning user
to the form with previous input.
Includes test to cover.
For #5195
- Adds filtering to the watched items list in notification preferences
so that deleted (recycle bin) items are removed via query.
- Adds relations and logic to properly remove watches upon user and
entity delete events, to old watches in database do not linger.
- Adds testing to cover the above.
Did not add migration for existing data, since patch will be close to
introduction, and lingering DB entries don't open a security concern,
just some potential confusion in specific potential scenarios.
Probably not work extra migration risk, although could add in future if
concerns/issues are found.
Related to #4499
