[Bug]: Old SMB external storage info is kept when changing configuration

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When changing the configuration of an SMB external storage, the previous configuration is kept in the database in oc_storages, together with all the metadata stored in oc_filecache about files in that external storage.

Steps to reproduce

1. Create an SMB external storage as an admin with "Global credentials, manually entered" as the authentication method.
2. User 1 sets their global credentials and accesses that external storage.
3. The admin modifies the configuration of that external storage and sets "Login and password" as the authentication method.

Expected behavior

The storage info for User 1 is removed from oc_storages and oc_filecache, since the authentication has changed and User 1 can no longer access it using their global credentials.

Nextcloud Server version

30

Start by tracing how changing an SMB external storage configuration updates oc_storages and related oc_filecache metadata. Reproduce the authentication-method change described in the issue, then verify that User 1's stored storage information and file metadata are removed when global credentials are no longer valid.