retry cluster creation when it fails

[gflarity]

What type of PR is this?

Test Infra

What this PR does / why we need it:

Occasionally E2E will fail to even create the test cluster:

2026-01-16T01:15:32.899Z	INFO	setup/shared_cluster.go:154	🚀 Setting up shared k3d cluster for all e2e tests...
2026-01-16T01:16:30.853Z	INFO	setup/k8s_clusters.go:453	✅ Cluster deleted successfully
2026-01-16T01:16:30.853Z	ERROR	tests/main_test.go:44	failed to setup shared cluster: failed to setup shared k3d cluster: failed to create cluster: Failed Cluster Start: Failed to add one or more agents: Node k3d-shared-e2e-test-cluster-agent-16 failed to get ready: error waiting for log line `successfully registered node` from node 'k3d-shared-e2e-test-cluster-agent-16': stopped returning log lines: node k3d-shared-e2e-test-cluster-agent-16 is running=true in status=restarting
FAIL	github.com/ai-dynamo/grove/operator/e2e/tests	57.982s

It's not clear why this would happen, and it happens very rarely. But what we can do is just retry like you would if you were creating the cluster by hand.

Also, sometimes the test can hang and take the full test timeout. This was fixed as well.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a API change?

NONE

Additional documentation e.g., enhancement proposals, usage docs, etc.: