Allow setting up a password after OIDC account creation. (Same for WebAuthn, which does not work; filed separately)

Feature request

Which Nextcloud Version are you currently using: (see administration page)

• [Nextcloud Hub 9] (30.0.12)
• OpenIDC 7.3.2

Is your feature request related to a problem? Please describe.

• Allow optional setting of password even after account creation by OIDC
• Problem to be solved: OIDC-Accounts do not allow to set up a password, not even by Admins

Describe the solution you'd like
Describe alternatives you've considered

• Several use cases require (now and then) that users can also login with their e-mail and password
• I tested the following is working, but I don't like the workaround:

1. As Admin, add manually an account for a new user X and give the Account name = OIDCLOGINPREFIX-<sub>.
2. For this trick, you as Admin need to know the <sub>.
3. Set up a start password for the new user X
4. When user X sub comes with OIDC, OIDC logs into the correct account.
5. User is now able to login either by OIDC or by e-mail (alternatively OIDCLOGINPREFIX-<sub>) and their password.
6. User is able to change the password

Additional context
I wish the OIDC App to allow setting a password even when no password has been assigned before the first OIDC-account-connect. The described trick works, but is ugly to perform and requires admin work.

No files, tests, or entry points are named. Start by tracing OIDC account creation and the existing password-setting flow, then reproduce the described admin and user scenarios. Done means an account created through OIDC can optionally set and later change a password while OIDC login continues to work.