Add "action" tag to /internal/allowed API

This allows us to re-use any other analytics that rely on the "action"
tag having a value set.

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.7.0 (unreleased)
+  - Transactions for /internal/allowed now have an "action" tag set
   - Method instrumentation now uses Module#prepend instead of aliasing methods
   - Repository.clean_old_archives is now instrumented
   - Add support for environment variables on a job level in CI configuration file

lib/api/internal.rb

@@ -23,9 +23,11 @@ module API
       end
 
       post "/allowed" do
+        Gitlab::Metrics.tag_transaction('action', 'Grape#/internal/allowed')
+
         status 200
 
-        actor = 
+        actor =
           if params[:key_id]
             Key.find_by(id: params[:key_id])
           elsif params[:user_id]
@@ -33,7 +35,7 @@ module API
           end
 
         project_path = params[:project]
-        
+
         # Check for *.wiki repositories.
         # Strip out the .wiki from the pathname before finding the
         # project. This applies the correct project permissions to