feat(gcloud): namespace prev_version by cluster on deploy

[jonathan-johnston]

Summary

For GKE deployments which are deployed to different clusters within the same workflow, referring to prev_version in a subsequent workflow step fails due to contention and overwrites. To resolve this we should namespace by cluster when storing the previous GKE deployment version.

Custom Checklist Items

Standard Checklist

• [x] My comments/docstrings/type hints are clear
• [x] I've tested this manually
• [x] The architecture diagrams have been updated, if need be
• [x] Any external changes/dependencies are linked and described
• [x] I've included any special rollback strategies above
• [x] Any relevant metrics/monitors/SLOs have been added or modified
• [x] I've notified all relevant stakeholders of the change
• [x] I've updated .github/CODEOWNERS, if relevant

[jonathan-johnston]

Running testing on this orb now.

Edit: tested and works as expected

[jonathan-johnston]

IMO this should be a major version bump because we'll have to point to the cluster-scoped prev_version when running our slack notifs.