Feature: API to get most used labels (#447)

* Add most-used labels API

* Filter conversation by labels

* Move match_all to any query

Co-authored-by: Pranav Raj S <pranavrajs@gmail.com>

app/controllers/api/v1/labels_controller.rb

@@ -2,4 +2,8 @@ class Api::V1::LabelsController < Api::BaseController
   def index # list all labels in account
     @labels = current_account.all_conversation_tags
   end
+
+  def most_used
+    @labels = ActsAsTaggableOn::Tag.most_used(params[:count] || 10)
+  end
 end