Auto-configure Discover from Wholphin server plugin (#2134)

## Description
https://github.com/damontecres/jellyfin-plugin-wholphin/pull/3 added a
new endpoint for Seerr configuration in Wholphin server plugin.

This PR adds support for reading that configuration and either
pre-filling the URL or automatically logging in.

Some code was copied from #1418 (thanks @matschi95!), but that PR worked
by inserting a DB record for the plugin provided server. Since the local
DB was preferred, this meant plugin config changes wouldn't be reflected
in the client. This PR instead attempts the connection and only updates
the in-memory connection state, so user switching and app restarts will
re-fetch from the plugin.

If the server plugin is not installed or no Seerr server is configured,
nothing in Wholphin changes.

### Related issues
#598 

This PR replaces #1418


### Testing
Emulator with different scenarios

## Screenshots
N/A

## AI or LLM usage
None

app/src/main/res/values/strings.xml

@@ -977,4 +977,6 @@
     <string name="home_settings_source_server_profile">Server user profile</string>
     <string name="home_settings_source_plugin">Server default</string>
     <string name="home_settings_source_web">User web client</string>
+    <string name="managed_by_server">Managed by server</string>
+    <string name="error">Error</string>
 </resources>