Updates to OSUserExecutor

* In `start()`, initialize from cache and hook models up. To accomplish this, we maintain a dictionary of seen identity models.
* Add error handling, with caching and removing from cache when request is successful or return an unretryable error.
* Requests will also maintain a flag called `sentToClient` to indicate if this request has been sent, and should not be flushed.
* Some request had extraneous fields so those are removed.

user execuor

exeuctor user

user exe

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalCore/Source/OneSignalCommonDefines.h

@@ -304,7 +304,8 @@ typedef enum {GET, POST, HEAD, PUT, DELETE, OPTIONS, CONNECT, TRACE, PATCH} HTTP
 #define OS_OPERATION_REPO_DELTA_QUEUE_KEY                                   @"OS_OPERATION_REPO_DELTA_QUEUE_KEY"
 
 // User Executor
-#define OS_USER_EXECUTOR_REQUEST_QUEUE_KEY                                  @"OS_USER_EXECUTOR_REQUEST_QUEUE_KEY"
+#define OS_USER_EXECUTOR_USER_REQUEST_QUEUE_KEY                             @"OS_USER_EXECUTOR_USER_REQUEST_QUEUE_KEY"
+#define OS_USER_EXECUTOR_TRANSFER_SUBSCRIPTION_REQUEST_QUEUE_KEY            @"OS_USER_EXECUTOR_TRANSFER_SUBSCRIPTION_REQUEST_QUEUE_KEY"
 
 // Identity Executor
 #define OS_IDENTITY_EXECUTOR_DELTA_QUEUE_KEY                                @"OS_IDENTITY_EXECUTOR_DELTA_QUEUE_KEY"