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>

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

@@ -15,6 +15,11 @@ class Api::V1::Accounts::InboxesController < Api::V1::Accounts::BaseController
     @campaigns = @inbox.campaigns
   end
 
+  def avatar
+    @inbox.avatar.attachment.destroy! if @inbox.avatar.attached?
+    head :ok
+  end
+
   def create
     ActiveRecord::Base.transaction do
       channel = create_channel