feat: add c2s websocket to identity server

foxchat/src/c2s/event.rs

@@ -17,9 +17,20 @@ pub enum Payload {
     },
     /// Hello message, sent after authentication succeeds
     Hello {
+        heartbeat_interval: u64,
         guilds: Vec<String>,
     },
     Identify {
         token: String,
     },
+    /// Sent on a regular interval by the client, to keep the connection alive.
+    Heartbeat {
+        #[serde(rename = "t")]
+        timestamp: u64,
+    },
+    /// Sent in response to a Heartbeat.
+    HeartbeatAck {
+        #[serde(rename = "t")]
+        timestamp: u64,
+    }
 }