support watch namespaces matched namespace selector (#7472)

skip caching namespaces at cluster scope if only watching single namespace

add --watch-namespace-selector in user guide

add e2e test

test/e2e-image/namespace-overlays/namespace-selector/values.yaml

@@ -0,0 +1,36 @@
+# TODO: remove the need to use fullnameOverride
+fullnameOverride: nginx-ingress
+controller:
+  image:
+    repository: ingress-controller/controller
+    tag: 1.0.0-dev
+    digest:
+  containerPort:
+    http: "1080"
+    https: "1443"
+
+  extraArgs:
+    http-port: "1080"
+    https-port: "1443"
+    # e2e tests do not require information about ingress status
+    update-status: "false"
+  ingressClassResource:
+    # We will create and remove each IC/ClusterRole/ClusterRoleBinding per test so there's no conflict
+    enabled: false
+  scope:
+    enabled: false
+    namespaceSelector: "foo=bar"
+
+  config:
+    worker-processes: "1"
+  service:
+    type: NodePort
+  admissionWebhooks:
+    enabled: false
+
+defaultBackend:
+  enabled: false
+
+rbac:
+  create: true
+  scope: false