Bug 2022743: Use 'async' for NimbusInterface.recordEventOrThrow [ci full]

[moztcampbell]

In order to actually propegate the errors to the caller, we need to run the coroutine with 'async' instead of 'launch'.

https://kotlinlang.org/docs/exception-handling.html#exception-propagation

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • This PR follows the breaking change policy:
    • We added this recently for fenix which has not started using it yet. This fixes for fenix needs.
• Quality: This PR builds and tests run cleanly
  • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
  • Consumer is fenix which will receive through nightly process automatically.
• Tests: This PR includes thorough tests or an explanation of why it does not
  • We don't currently have the ability to force recordEvent failures with current interface.
• Changelog: This PR includes a changelog entry in CHANGELOG.md or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• Dependencies: This PR follows our dependency management guidelines
  • N/A

[moztcampbell]

I did manual testing with Fenix by adding a use of this API, and modifying the underlying recordEvent to throw an exception. I was able to confirm that changing 'launch' to 'async' turns exception into a catchable one as desired.