feat(gateway): add stopGateway function (#2078)

* Move the shard stopping to gatewayManager in order to stop the gateway standalone.

* Update gateway/gateway_manager.ts

Co-authored-by: ITOH <to@itoh.at>

* Update gateway/stopGateway.ts

Co-authored-by: ITOH <to@itoh.at>

* Update gateway/stopGateway.ts

* Update gateway/stopGateway.ts

* Update gateway/stopGateway.ts

Co-authored-by: ITOH <to@itoh.at>
Co-authored-by: Skillz4Killz <23035000+Skillz4Killz@users.noreply.github.com>

gateway/gateway_manager.ts

@@ -18,6 +18,7 @@ import {
 import { resume } from "./resume.ts";
 import { sendShardMessage } from "./sendShardMessage.ts";
 import { prepareBuckets, spawnShards } from "./spawnShards.ts";
+import { stopGateway } from "./stopGateway";
 import { tellWorkerToIdentify } from "./tellWorkerToIdentify.ts";
 import { DiscordenoShard } from "./shard.ts";
 
@@ -88,6 +89,7 @@ export function createGatewayManager(
     handleOnMessage: options.handleOnMessage ?? handleOnMessage,
     processGatewayQueue: options.processGatewayQueue ?? processGatewayQueue,
     closeWS: options.closeWS ?? closeWS,
+    stopGateway: options.stopGateway ?? stopGateway,
     sendShardMessage: options.sendShardMessage ?? sendShardMessage,
     resume: options.resume ?? resume,
     safeRequestsPerShard: options.safeRequestsPerShard ?? safeRequestsPerShard,
@@ -209,6 +211,8 @@ export interface GatewayManager {
   processGatewayQueue: typeof processGatewayQueue;
   /** Closes shard WebSocket connection properly. */
   closeWS: typeof closeWS;
+  /** Use this function to stop the gateway properly. */
+  stopGateway: typeof stopGateway;
   /** Properly adds a message to the shards queue. */
   sendShardMessage: typeof sendShardMessage;
   /** Properly resume an old shards session. */