Add Confluent-Client-Version header to requests to SR, Python client

[fangnx]

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: https://confluentinc.atlassian.net/browse/DGS-22770

Test & Review

Open questions / Follow-ups