properly fix patching /credentials sub-paths

[hperl]

Ideally, for both create, patch, and PUT operations, the following should be implemented with proper
validation:

1. Passwords:

   • Set or change passwords (with validation ensuring the hash or plaintext password is correct).
   • Delete passwords.

2. OIDC:

   • Set or change OIDC subject and provider.
   • Delete OIDC subject and provider.

3. WebAuthn and Passkey Credentials:

   • Set, change, or delete WebAuthn and passkey credentials (e.g., to import passkey users).

4. Code Credentials:

   • Activate or deactivate code credentials.

5. TOTP:

   • Set, change, or delete TOTP configurations.

6. Lookup Secrets:

   • Set, change, or delete lookup secrets.

Restrictions:
What should not be allowed is:

• Adding arbitrary keys to the config object.
• Changing identifiers that are typically set by the system.
• Modifying keys that should only be set by the system.

Originally posted by @aeneasr in #4277 (comment)