Fix RBAC for getting started

Namespace was wrong in clusterrolebinding. Instead of default which
is used in examples, we need getting started namespace.

docs/getting-started/rbac/admin-role.yaml

@@ -0,0 +1,29 @@
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: tekton-triggers-example-sa
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: triggers-example-eventlistener-binding
+subjects:
+- kind: ServiceAccount
+  name: tekton-triggers-example-sa
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: tekton-triggers-eventlistener-roles
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRoleBinding
+metadata:
+  name: triggers-example-eventlistener-clusterbinding
+subjects:
+- kind: ServiceAccount
+  name: tekton-triggers-example-sa
+  namespace: getting-started
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: tekton-triggers-eventlistener-clusterroles