Clear latest schema caches after schema registration

[Oliver Bennett (omwbennett)]

What

When a schema is registered invalidate that subject's entries in the latest-version and latest-with-metadata caches. Re-use the existing clear_latest_caches() method to do this.

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

This addresses the second bug reported in #1950

Test & Review

Added unit tests and did some manual testing locally.

Open questions / Follow-ups

[confluent-cla-assistant]

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✅ omwbennett
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[Oliver Bennett (omwbennett)]

Please sign the Contributor License Agreement here before this PR can be approved.❌ omwbennettPlease push an empty commit if you would like to re-run the checks to verify CLA status for all contributors.

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