Fixes issue where certain errors would not show to the user
due to extra navigation jumps which lost the error message
in the process.
This simplifies and aligns exceptions with more directly
handled exception usage at the controller level.
Fixes#3264
- Required extracting logic into repo.
- Changed some existing creation paths to standardise behaviour.
- Added test to cover new endpoint.
- Added extra test for user delete to test migration.
- Changed how permission errors are thrown to ensure the right status
code can be reported when handled in API.
- Reduced the amount of different exceptions from LDAP attempt so they
can be handled more consistently.
- Added test to cover.
- Also cleaned up LDAP tests to reduce boilterplate mocks.
Fixes#2048
