fix(datastore): Prevent stop from interrupting subsequent start call

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:
#1690

Description of changes:

• Ensure that a websocket that is in the process of being closed is not re-used to start new subscriptions. This fixes the following code sample from our docs:

Amplify.DataStore.stop(
        {
            Amplify.DataStore.start(
                { Log.i("MyAmplifyApp", "DataStore started") },
                { Log.e("MyAmplifyApp", "Error starting DataStore", it) }
            )
        },
        { Log.e("MyAmplifyApp", "Error clearing DataStore", it) }
    )

NB: There is a caveat that this fix works as expected for the above code snippet, but it does not necessarily work if there are multiple levels of stop/start calls nested within each other.

How did you test these changes?

• Verified that calling start from the stop callback now starts all subscriptions as normal.

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #2569 (b45a1ae) into main (be07335) will increase coverage by 0.00%.
The diff coverage is 50.00%.

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