Show erasure status when listing users in the Admin API (#14205)

* Show erasure status when listing users in the Admin API

* Use USING when joining erased_users

* Add changelog entry

* Revert "Use USING when joining erased_users"

This reverts commit 30bd2bf106415caadcfdbdd1b234ef2b106cc394.

* Make the erased check work on postgres

* Add a testcase for showing erased user status

* Appease the style linter

* Explicitly convert `erased` to bool to make SQLite consistent with Postgres

This also adds us an easy way in to fix the other accidentally integered columns.

* Move erasure status test to UsersListTestCase

* Include user erased status when fetching user info via the admin API

* Document the erase status in user_admin_api

* Appease the linter and mypy

* Signpost comments in tests

Co-authored-by: Tadeusz Sośnierz <tadeusz@sosnierz.com>
Co-authored-by: David Robertson <david.m.robertson1@gmail.com>