fix: memory leak in AppSyncWebSocketClient (#41)

Description of changes:
WebSocketTransport holds a strong reference to AppSyncWebSocketClient, and vice versa. This causes a retain cycle that can be solved by making AppSyncWebSocketClient's reference weak.

Testing:
Verified solution via memory graph debugger.

Co-authored-by: Anthony Guella <anthkgue@audible.com>

Author: anthonyguella

Sources/AWSAppSyncApolloExtensions/Websocket/AppSyncWebSocketClient.swift

@@ -17,7 +17,7 @@ public class AppSyncWebSocketClient: NSObject, ApolloWebSocket.WebSocketClient,
 
     // MARK: - ApolloWebSocket.WebSocketClient
 
-    public var delegate: ApolloWebSocket.WebSocketClientDelegate?
+    public weak var delegate: ApolloWebSocket.WebSocketClientDelegate?
     public var callbackQueue: DispatchQueue
 
     private let requestLock = NSLock()