Update tests to use OAuth 2 with Keycloak

Author: sbernauer

tests/templates/kuttl/iceberg-rest/22-assert.yaml

@@ -0,0 +1,12 @@
+---
+apiVersion: kuttl.dev/v1beta1
+kind: TestAssert
+timeout: 300
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: keycloak
+status:
+  readyReplicas: 1
+  replicas: 1

tests/templates/kuttl/iceberg-rest/22-install-keycloak.yaml

@@ -0,0 +1,5 @@
+---
+apiVersion: kuttl.dev/v1beta1
+kind: TestStep
+commands:
+  - script: envsubst < 22_keycloak.yaml | kubectl apply -n $NAMESPACE -f -