Add WebSocket client ping implementation (#30293)

This commit introduces new functionality on the client side to send PING messages over the websocket. If the server doesn't respond within PING_INTERVAL (currently 30 seconds), the connection is closed and re-created. This will allow us to find broken connections more quickly.

webapp/channels/src/components/post_view/post_body_additional_content/__snapshots__/post_body_additional_content.test.tsx.snap

@@ -100,6 +100,7 @@ exports[`PostBodyAdditionalContent with a normal link Should render the plugin c
         "closeCallback": null,
         "closeListeners": Set {},
         "config": Object {
+          "clientPingInterval": 30000,
           "maxWebSocketFails": 7,
           "maxWebSocketRetryTime": 300000,
           "minWebSocketRetryTime": 3000,
@@ -118,6 +119,7 @@ exports[`PostBodyAdditionalContent with a normal link Should render the plugin c
         "messageListeners": Set {},
         "missedEventCallback": null,
         "missedMessageListeners": Set {},
+        "pingInterval": null,
         "postedAck": false,
         "reconnectCallback": null,
         "reconnectListeners": Set {},
@@ -156,6 +158,7 @@ exports[`PostBodyAdditionalContent with a normal link Should render the plugin c
         "closeCallback": null,
         "closeListeners": Set {},
         "config": Object {
+          "clientPingInterval": 30000,
           "maxWebSocketFails": 7,
           "maxWebSocketRetryTime": 300000,
           "minWebSocketRetryTime": 3000,
@@ -174,6 +177,7 @@ exports[`PostBodyAdditionalContent with a normal link Should render the plugin c
         "messageListeners": Set {},
         "missedEventCallback": null,
         "missedMessageListeners": Set {},
+        "pingInterval": null,
         "postedAck": false,
         "reconnectCallback": null,
         "reconnectListeners": Set {},