Reassigning mentors sends a notification to their mentees.
The table listing relations between mentors and mentees lists a mentor for everyone who hasn't opted-out mentorship.
Sometimes these mentees are not aware of the existence of their mentor until they get a notification about their new mentor. It creates surprise.
Following what was done for T335462: Claim mentee sends notification to users without access to mentorship, we should have stricter rules when reassigning mentors.
We shouldn't send a reassignment notification to:
- accounts who opted-out mentorship (already covered)
- accounts created before mentorship deployment at a given wiki, except if they visited their homepage
- accounts who never accessed their homepage