Implement async context manager protocol for AIO clients

[lpsinger]

When AIOProducer or AIOConsumer is used as the target of a with: statement, automatically close the connection at the end of the context.

What

Checklist

• Contains customer facing changes? Including API/behavior changes
• Did you add sufficient unit test and/or integration test coverage for this PR?
  • If not, please explain why it is not required

References

JIRA:

Test & Review

Open questions / Follow-ups

[confluent-cla-assistant]

🎉 All Contributor License Agreements have been signed. Ready to merge.
✅ lpsinger
_{Please push an empty commit if you would like to re-run the checks to verify CLA status for all contributors.}