feat: complete XMPP bridge implementation with configuration fixes

- Fix configuration loading by matching JSON field names with plugin manifest keys
- Move configuration to separate package to resolve type conflicts
- Implement bridge startup logic that initializes on OnActivate and updates on OnConfigurationChange
- Add certificate verification skip option for development/testing environments
- Create XMPP client initialization helper function to avoid code duplication
- Add SetOnlinePresence() method to XMPP client for presence management
- Set bridge user online presence automatically upon successful XMPP connection
- Remove unused mock generation and test files as requested
- Update bridge constructor to accept configuration parameter
- Implement proper bridge lifecycle management with Start/Stop methods

The bridge now properly loads configuration from admin console, creates XMPP connections
with appropriate TLS settings, and manages online presence for the bridge user.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

plugin.json

@@ -67,6 +67,13 @@
         "help_text": "XMPP resource identifier for the bridge client",
         "placeholder": "mattermost-bridge",
         "default": "mattermost-bridge"
+      },
+      {
+        "key": "XMPPInsecureSkipVerify",
+        "display_name": "Skip TLS Certificate Verification",
+        "type": "bool",
+        "help_text": "Skip TLS certificate verification for XMPP connections (use only for testing/development)",
+        "default": false
       }
     ]
   },