feat: upgrade/downgrade support and version tracking

[lioraron]

Context

The E2E Testing Responsibilities document requires module operators to support and test upgrade/downgrade scenarios.

Related: RHOAIENG-63969
Depends on: #70

Integration model

The RHOAI platform operator does not manage batch-gateway-operator directly. The integration chain is:

Platform operator → ai-gateway-operator (module) → batch-gateway-operator (sub-operator)

Upgrade orchestration (DAG ordering, upgrade gates, version tracking) is the platform operator's contract with ai-gateway-operator. Batch-gateway-operator's upgrade requirements should be defined by the ai-gateway-operator team — specifically, how they coordinate sub-operator upgrades and what version metadata they need.

Potentially needed (pending ai-gateway-operator team input)

Version tracking

Populate .status.releases with version metadata so ai-gateway-operator can track which version is running.

Upgrade e2e test

Test that rolling from version N to N+1 does not cause data loss and operands transition cleanly.

Downgrade e2e test

Test that rollback to version N works correctly.

platformVersion transitions

Test that platformVersion transitions cleanly during upgrades.

What's already implemented

• Helm values include image tags (parsed from operator env vars in production)
• ConfigMaps have checksums and Deployment pod templates include checksum/config annotation for rollouts
• No .status.releases field exists yet (see feat: implement PlatformObject interface for RHOAI module integration #70)