Fix deadlock in sqlite Connection.sync by moving publishers off of "SQLite.Database" queue (#1406)

Author: ashiemke

AmplifyPlugins/DataStore/AWSDataStoreCategoryPlugin/Sync/SubscriptionSync/ReconcileAndLocalSave/ReconcileAndLocalSaveOperation.swift

@@ -126,6 +126,7 @@ class ReconcileAndLocalSaveOperation: AsynchronousOperation {
         do {
             try storageAdapter.transaction {
                 queryPendingMutations(forModelIds: remoteModelIds)
+                    .subscribe(on: workQueue)
                     .flatMap { mutationEvents -> Future<([RemoteModel], [LocalMetadata]), DataStoreError> in
                         let remoteModelsToApply = self.reconcile(remoteModels, pendingMutations: mutationEvents)
                         return self.queryLocalMetadata(remoteModelsToApply)