[feature] Allow expired-password users with social login to remove their Django password

⚠️ Not suitable for beginners

Is your feature request related to a problem? Please describe.
An admin user can have both a local Django password and a connected social account. When password expiration is enabled and the local password expires, the user is forced into the password-change flow even if they intend to use social login only.

Describe the solution you'd like
When an authenticated admin user reaches the expired-password flow and already has at least one connected social account, show an additional option to remove the Django password entirely.

If the user chooses this option:

• the local Django password should be cleared or replaced with an unusable password,
• the account should remain connected to the existing social account(s),
• future logins should rely only on social authentication,
• the user should not be prompted again to update a password for password-based authentication.

This would be especially useful for admins who initially signed up with email/password and later migrated to SSO-only access.

Additional context
Relevant behavior already exists for password expiration redirect and password update flows in the admin and account views, so this feature would extend the current expired-password handling rather than replace it.

Trace the existing expired-password redirect and password-update flows in the admin and account views. Add an option for authenticated users with connected social accounts to remove the Django password while preserving social connections, then verify that future logins use social authentication without another password-update prompt.