Facebook Plugin : need a public url for callback

[mikbry]

Describe the bug
We need a callback url available for Fb messenger services to access backend.

To Reproduce
Steps to reproduce the behavior:

1. Install Opla using docker composer
2. Create a user and a chatbot
3. Go to admin, select extensions
4. Add messaging platforms
5. Select fb-messenger
6. callback url display: "url://" and can't be modified

Expected behavior
A clear indication that we need a public url for Fb messenger services. And how to create one or a new popup to edit it. And advanced public url can't be modified.