[FEATURE] Helm chart CI on kind: install, staged upgrade, rollback, repeated sync #3687

Proves the charts follow the version skew policy and behave under Argo CD.

Tracks "Test the charts in CI" in the Helm Charts workstream of the Extensible Install Roadmap.

Required changes. On kind, CI:

• installs the charts;
• upgrades from the previous release stage by stage in the version skew policy's order, and rolls back;
• renders and applies twice, as Argo CD does.

Override Helm's default rollback and deletion behaviour: the version skew policy does not roll back its last step and keeps earlier SandboxConfigs.

Dependencies: #3682, #3684, #3685.

Enforcement: key Secrets are unchanged, and the previous release's SandboxConfig survives.

Parent Issue: #3170