feat: Ability to remove inbox avatar (#2885)

* Delete inbox avatar

1) New API endpoint added for deleting inbox avatar.
2) Delete avatar button in the inbox settings page.

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

config/routes.rb

@@ -102,6 +102,7 @@ Rails.application.routes.draw do
             get :campaigns, on: :member
             get :agent_bot, on: :member
             post :set_agent_bot, on: :member
+            delete :avatar, on: :member
           end
           resources :inbox_members, only: [:create, :show], param: :inbox_id
           resources :labels, only: [:index, :show, :create, :update, :destroy]