Add REST API quota checks

This commit adds quota groups for all REST API calls. This enables
enforcer implementations to throttle specific calls.

Change-Id: Ideb182015519acecfbe304ef6a80ef38c854fb03
diff --git a/Documentation/rest-api.txt b/Documentation/rest-api.txt
index 8f6a47b..a8ab353 100644
--- a/Documentation/rest-api.txt
+++ b/Documentation/rest-api.txt
@@ -191,6 +191,11 @@
 "`422 Unprocessable Entity`" is returned if the ID of a resource that is
 specified in the request body cannot be resolved.
 
+==== 429 Too Many Requests
+"`429 Too Many Requests`" is returned if the request exhausted any set
+quota limits. Depending on the exhausted quota, the request may be retried
+with exponential backoff.
+
 [[tracing]]
 === Request Tracing
 For each REST endpoint tracing can be enabled by setting the