Migrate Watcher to Use OpenStackSDK

Watcher currently uses individual Python client libraries (python-novaclient, python-cinderclient, etc.) to interact with other OpenStack services. These client libraries have been frozen or deprecated and are scheduled for removal in future OpenStack releases. This blueprint tracks the migration of Watcher to use OpenStackSDK, the unified and officially maintained SDK for OpenStack service interactions, ensuring long-term maintainability and support.

Phase 1 (2026.1) focuses on:
- Establishing OpenStackSDK infrastructure
- Migrating Nova client to SDK compute proxy
- Creating migration patterns for subsequent phases

Future phases will migrate remaining clients (Cinder, Keystone,Placement, Ironic) and eventually integrate Watcher itself into OpenStackSDK as an infra_optim service. After that, we can remove usage of the current python-watcherclient implementation before deprecating it an removing.