Create Stackdriver module and inject it into backend module

This adds Stackdriver as a DI module into the registry codebase. This is a
necessary prerequisite for using Stackdriver based monitoring. For now, I'm
only adding it to the backend module as it will be more work to add it to the
frontend module.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=126730925

google/monitoring/BUILD

@@ -0,0 +1,11 @@
+package(default_visibility = ["//visibility:public"])
+
+java_library(
+    name = "monitoring_java_lib",
+    exports = [
+        "@google_api_services_monitoring//jar",
+    ],
+    runtime_deps = [
+        "@google_api_client//jar",
+    ],
+)