Add a flag for multi-namespace setup (#132)

Author: kyessenov

proxy/v1/config/proxy_mesh.proto

@@ -74,6 +74,12 @@ message ProxyMeshConfig {
   // Connection timeout used by Envoy. (MUST BE >=1ms)
   google.protobuf.Duration connect_timeout = 11;
 
+  // Kubernetes namespace to be monitored by Istio control plane.
+  // This can be a single application namespace (e.g. "bookinfo") or
+  // left unspecified, in which case all Kubernetes namespaces are
+  // observed.
+  string application_namespace = 13;
+
   // Class of ingress resources to be processed by Istio ingress
   // controller.  This corresponds to the value of
   // "kubernetes.io/ingress.class" annotation.