DefaultProvider field does not strip whitespace

[alexander-bauer]

Describe the bug
This is a minor behavioral change, but can be pretty hard to troubleshoot, and have major implications.

The DefaultProvider field, and possibly other fields, do not strip whitespace from the outside ends of user input. This can result in behavior including unexpectedly preventing password login

To Reproduce
Steps to reproduce the behavior:

In the SSO admin interface, configure a DefaultProvider with a leading or trailing space. The resulting configuration (retrieved via API) will retain that space.

{
  "keycloak": {
    ...
    "DefaultProvider": " Jellyfin.Server.Implementations.Users.DefaultAuthenticationProvider",
  }
}

Expected behavior
Leading and trailing whitespace should be stripped.

Versions (please complete the following information):

• OS: Kubernetes on K3OS
• Browser: Firefox
• Jellyfin Version: 10.8.4
• Plugin Version: 3.4.0.0