Add breaking email restrictions checker in doctor (#19903)
Add breaking email restrictions checker in doctor (#19903)

* Add breaking change check in doctor

- This patch introduces a new kind of doctor type, breaking. This file
is made to register checks that helps with detecting when a breaking
change might impact a Gitea instance.
- For now the only check here(and the reason of creating this) is to
check if all users in the database has a valid email address, which
might not be the case after
https://github.com/go-gitea/gitea/pull/17688. This _simply_ uses the
validation function to detect and report these cases.
- Helps admins with detecting #19897.
- I have no clue which priority should be and IsDefault is true, because
when breaking change happen and we have a doctor check for it, we can
say "run `gitea doctor` to help you with this and maybe you find other
errors :wink:".

* Makes no sense tbh

* Fix copyright

* Update modules/doctor/breaking.go

Co-authored-by: Lunny Xiao <0b0704cdf8f0790c6f1df1f74c38be95a8917ed2@gmail.com>

Co-authored-by: techknowlogick <ff3785bfdd6690916cd886199c6b899e5f93e2e2@mdranta.net>
Co-authored-by: Lunny Xiao <0b0704cdf8f0790c6f1df1f74c38be95a8917ed2@gmail.com>
Co-authored-by: techknowlogick <274271a2414b6bd0d2eb0401dd4ff6e85d7016a7@gitea.io>
go-gitea/gitea,go-gitea/gitea,go-gitea/gitea