Grant required IAM roles to Compute Engine default SA when --managed-mldiagnostics is passed during xpk cluster create

[rapatchi]

When provisioning clusters with --managed-mldiagnostics, XLA ML diagnostics requires roles/hypercomputecluster.editor, roles/storage.objectUser, and roles/logging.logWriter to be bound to the Compute Engine default service account.

This commit:

1. Automatically resolves projectNumber and grants these 3 required IAM roles via gcloud projects add-iam-policy-binding during cluster create when --managed-mldiagnostics is enabled.
2. Updates user documentation (permissions.md, clusters.md) and unit test coverage accordingly.

Issue

If not done permissions need to be given manually for mldiagonstics to work.

Testing

Have you performed any manual testing on your change?

Prior IAM Bindings:

Cluster Creation Logs:

(xpk_local_venv) rapatchi@rapatchi2:~/xpk_fork/xpk_sa$ xpk cluster create --cluster=maxtest-cluster1 --tpu-type=v5litepod-8 --project=rapatchiconsumer --zone=us-central1-b --num-nodes=2 --spot --managed-mldiagnostics
[XPK] Starting xpk v0.1.dev903+g2b0dc6334
...
[XPK] Task: `Get Project Number` is implemented by `gcloud projects describe rapatchiconsumer --format="value(projectNumber)"`
[XPK] Granting necessary roles to 641919595434-compute@developer.gserviceaccount.com
[XPK] Task: `Grant roles/hypercomputecluster.editor` is implemented by `gcloud projects add-iam-policy-binding rapatchiconsumer --member="serviceAccount:641919595434-compute@developer.gserviceaccount.com" --role="roles/hypercomputecluster.editor" --condition=None`
[XPK] Task: `Grant roles/hypercomputecluster.editor` succeeded.
[XPK] Task: `Grant roles/storage.objectUser` is implemented by `gcloud projects add-iam-policy-binding rapatchiconsumer --member="serviceAccount:641919595434-compute@developer.gserviceaccount.com" --role="roles/storage.objectUser" --condition=None`
[XPK] Task: `Grant roles/storage.objectUser` succeeded.
[XPK] Task: `Grant roles/logging.logWriter` is implemented by `gcloud projects add-iam-policy-binding rapatchiconsumer --member="serviceAccount:641919595434-compute@developer.gserviceaccount.com" --role="roles/logging.logWriter" --condition=None`
[XPK] Task: `Grant roles/logging.logWriter` succeeded.
[XPK] Task: `Determine server supported GKE versions for default gke version` is implemented by `gcloud container get-server-config --project=rapatchiconsumer --region=us-central1 --flatten="channels" --filter="channels.channel=RAPID" --format="value(channels.defaultVersion)"`
...

Post Creation:

Have you verified use cases affected by goldens? Yes

[scaliby]

thanks for addressing my feedback. LGTM!

[scaliby]

Please address linter failures and resolve conflicts

[rapatchi]

Addressed the linter fix and merge conflict. Will wait for presubmits to pass.