add sr-version to sr client API

[gzimmers-cflt]

What

No breaking changes, adding an existing endpoint to the client interface and implementing in local and cached clients.

Checklist

Please answer the questions with Y, N or N/A if not applicable.

• [ Y ] Contains customer facing changes? Including API/behavior changes
• [ N ] Is this change gated behind config(s)?
  • List the config(s) needed to be set to enable this change
• [ Y ] Did you add sufficient unit test and/or integration test coverage for this PR?
  • If not, please explain why it is not required
• [ N ] Does this change require modifying existing system tests or adding new system tests?
  • If so, include tracking information for the system test changes
• [ N ] Must this be released together with other change(s), either in this repo or another one?
  • If so, please include the link(s) to the changes that must be released together

References

JIRA:

Adding existing sr version GET to clients for easier access.
https://confluentinc.atlassian.net/browse/DGS-21658

Test & Review

The new code was tested using unit tests.

Open questions / Follow-ups

NA

[confluent-cla-assistant]

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[rayokota]

Thanks @gzimmers-cflt , LGTM