tests: add a test to validate pause and resume feature

[darthsuburbus]

Description

Add a e2e test that tests out the pause and resume functionality implemented in #82:

1. Create a Pod with a PVC and some generated data.
2. Scale the replicas to 0, controller should delete the pod associated with the sandbox.
3. Sandbox CR should remain consistent.
4. Scale the replicas to 1, the controller will recreate the pod. Verify that the data is intact on the PVC.

This test addresses the request made in #248.

Testing Done

   pvc_persistence_test.go:68: WaitForObjectNotFound *v1.Namespace (/pvc-persistence-test-1772168327331581080) took 43.463444028s
--- PASS: TestPVCPersistenceAcrossReplicas (89.90s)

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[vicentefb]

In your WaitForObject calls, you are asserting the exact Message string inside the Conditions array (e.g., "Pod does not exist, replicas is 0; Service Exists" and "Pod is Ready; Service Exists").
While these strictly match the controller's current output, testing against exact human-readable message strings is generally an anti-pattern in K8s e2e tests.

Suggestion: Modify your predicates.SandboxHasStatus (or create a new predicate) to only assert against Type, Status, and Reason. The Reason field (DependenciesReady / SandboxNotReady) is meant for programmatic consumption for example.

[vicentefb]

nit: could we drop this down to 50Mi or 100Mi to be gentler on the test cluster's dynamic provisioner, depending on your storage class's minimums ?

[vicentefb]

Currently, execWriteFileToPod and execReadFileFromPod use os/exec to invoke the local kubectl CLI. This introduces an environmental dependency on the test runner's kubectl binary and kubeconfig, which can lead to flaky tests in CI. Looking at the rest of our e2e test suite (like shutdown_test.go), we consistently rely on the client-go API via our test framework and avoid shelling out to external binaries.

Suggestion: Let's keep this test pure-Go and self-contained by using client-go to execute the read/write commands directly against the API server.

[vicentefb]

Thanks! This is a very valuable test that was missing. Overall, the logic is very solid. You're correctly simulating the exact behavior the controller executes when Replicas hits 0 (where it deletes the pod but retains the Sandbox CR and PVCs ), and then successfully validating the recovery. Left some comments.