Chore: API to get conversations count (#808)

Addresses: #497

app/controllers/api/v1/accounts/conversations_controller.rb

@@ -8,6 +8,11 @@ class Api::V1::Accounts::ConversationsController < Api::BaseController
     @conversations_count = result[:count]
   end
 
+  def meta
+    result = conversation_finder.perform
+    @conversations_count = result[:count]
+  end
+
   def create
     @conversation = ::Conversation.create!(conversation_params)
   end

app/views/api/v1/accounts/conversations/meta.json.jbuilder

@@ -0,0 +1,7 @@
+json.data do
+  json.meta do
+    json.mine_count @conversations_count[:mine_count]
+    json.unassigned_count @conversations_count[:unassigned_count]
+    json.all_count @conversations_count[:all_count]
+  end
+end