Cloud Run runtime: implement service lifecycle (deploy/stop/delete/list) via Admin API

[scion-gteam]

Summary

Implement the Cloud Run service lifecycle for CloudRunRuntime via the Cloud Run Admin API.

Context

PR #345 (epic #169, storage provisioning PR3) landed the broker-side provisioning + mount-realization path for Cloud Run, but deliberately deferred the actual service lifecycle. Today pkg/runtime/cloudrun_runtime.go provisions the workspace and then returns:

cloudrun: Run not yet implemented — workspace provisioned, but Cloud Run service deployment requires the Admin API (follow-up PR)

Run, Stop, Delete, and List are "not yet implemented" stubs.

Work

• Implement Run to deploy a Cloud Run service via the Admin API, referencing the realized MountDescriptor (cloudrun-volume or NFS mount) produced by the Tier-3 backends.
• Implement Stop / Delete / List against the Admin API.
• Add exec/logs access as appropriate for the Cloud Run model.
• Tests covering the deploy/teardown wiring (fake/mocked Admin API).

References

• Epic fix(runtime/k8s): specify container on PodExec calls #169
• PR Storage provisioning PR3: Cloud Run runtime + Tier-3 mount types (issue 169) #345 (Cloud Run runtime + Tier-3 mount types)