fix(Analytics): Fixing crash when attempting to submit events while a previous submission is in progress

[ruisebas]

Issue #

• Amplify version 2.12, EventRecorder causes crashed app issue when submit event #3328

Description

This PR fixes a crash that was happening when EventRecorder.submitAllEvents() was called while a previous submission was still ongoing.
This happened because the submittedEvents array was being populated by the previous submission, while the very first thing a new one does is to set it to [].

I am changing the behaviour so that submitAllEvents now waits until the previous submission ends before continuing. I've explored just using a lock to manipulate the array instead, but while that did fix the crash, it would still produce undetermined behaviour when the array was emptied.

General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

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