[Bug] Enable HTTP Cache-Control in python-zvm-sdk

[dvjsharma]

Summary

The python-zvm-sdk client does not set any HTTP cache headers on REST API calls, causing intermediary caches (proxies, CDNs) to return stale “still creating…” or outdated data. Similar to Nova’s RFC 7234 issue, the SDK must explicitly control caching via Cache-Control/ETag headers to ensure real-time resource state is returned.

Launchpad ref - https://bugs.launchpad.net/python-zvm-sdk/+bug/1748191
Nova Launchpad ref - https://bugs.launchpad.net/nova/+bug/1747935