Fix an issue with empty username when user creation disrupted

[Anexen]

Description

If for some reason the user creation is interrupted in the middle, the user with an empty username remains in the database. This makes the account unusable and prevents the creation of new users with the following error:

UniqueViolation: duplicate key value violates unique constraint "auth_user_username_key"
DETAIL:  Key (username)=() already exists.

This PR resolves this issue and also decreases the number of database queries when a user logs in.

Contains

• Breaking Changes
• New/Update documentation
• CI/CD modifications

Changes

• Fix an issue with empty username when user creation disrupted
• Reduce the number of database queries when user logs in.

[chrismaille]

Hi @Anexen, thank you for the contribution.

Can you give, in more details, the user creation interruption you got? Did you change anything on standard user model behavior in your project?

[Anexen]

@chrismaille, I didn't change the standard user model. I think there was a network issue somewhere between user_model.objects.get_or_create and subsequent user.save(). For instance, if the check_first_super_user function failed due to a timeout, it could leave the user with an empty username in the database, thereby preventing the creation of new users.