Users created without email cannot save user settings

## What

admin user-create treats email as optional, but user-settings requires it so users with empty email cannot save (e.g. locale). #25096 explicitly Closes #21946.

## Want

- Admin user-create treats email as optional, but user-settings requires it so users with empty email cannot save (e.g. locale)
- #25096 explicitly Closes #21946

## Ideas this came from

- [#21946 Email address optional in user creation dialogue, but not in the user settings](https://github.com/goauthentik/authentik/issues/21946) — When creating a new user through the admin web-interface (https://

Start by reviewing the behavior described in issues #25096 and #21946, then reproduce it through the admin user-creation and user-settings pages with an empty email. Done means a user created without an email can save a settings change such as locale.

Written by the indexing model from the issue text.