feat(datastore): refactor DataStore to use Async APIs from APIPlugin #48

Job	Run time
Build Amplify Swift for tvOS / Build Amplify-Build \| tvOS	11m 9s
Build Amplify Swift for macOS / Build Amplify-Build \| macOS	7m 6s
Build Amplify Swift for watchOS / Build Amplify-Build \| watchOS	9m 49s
Build Amplify Swift for iOS / Build Amplify-Build \| iOS	6m 4s
Confirm Passing Build Steps	1s
	34m 9s

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