feat: Implement IRC Gateway Service and related functionality

- Add IrcGatewayService to handle IRC connections and commands.
- Create IrcMessage class for parsing IRC protocol lines.
- Implement IrcMessageFormatter for formatting messages as IRC lines.
- Define IrcNumericReply constants for IRC numeric replies.
- Add IrcOptions class for configuration settings related to IRC.
- Create IrcServiceExtensions for adding IRC services to the application.
- Refactor ChannelsController to use IChatService for broadcasting messages and channel updates.
- Update ChatHub to utilize IChatService for user connection and message handling.
- Introduce ChatService to manage chat-related operations and interactions.
- Implement SignalRBroadcaster for broadcasting messages to SignalR clients.
- Update PresenceTracker to retrieve usernames for connections.
- Modify appsettings.example.json to include IRC configuration options.
- Update solution file to include the new IRC project.

src/EchoHub.Server/appsettings.example.json

@@ -14,6 +14,16 @@
     "PublicServer": false,
     "PublicHost": ""
   },
+  "Irc": {
+    "Enabled": false,
+    "Port": 6667,
+    "TlsEnabled": false,
+    "TlsPort": 6697,
+    "TlsCertPath": "",
+    "TlsCertPassword": "",
+    "ServerName": "echohub",
+    "Motd": "Welcome to EchoHub IRC Gateway!"
+  },
   "Serilog": {
     "MinimumLevel": {
       "Default": "Information",