CloudMonitoring: Initial GCM Schema (#67739)

* Initial GCM schema work

- Split types for convenience
- Update conditionals where needed
- Update type references

* Add additional supporting types

* Add some more accessory and legacy types

* Add missing type

* Rename backend folder

* Add missing generated file

* Review

.github/pr-commands.json

@@ -89,7 +89,7 @@
   },
   {
     "type": "changedfiles",
-    "matches": [ "public/app/plugins/datasource/cloud-monitoring/**/*", "pkg/tsdb/cloudmonitoring/**/*"],
+    "matches": [ "public/app/plugins/datasource/cloud-monitoring/**/*", "pkg/tsdb/cloud-monitoring/**/*"],
     "action": "updateLabel",
     "addLabel": "datasource/GoogleCloudMonitoring"
   },