[Facebook] Replace `fbchat` service with service based on `messenger-api-python`

Hi there,

coming from @orzechszek's request at #485, we may want to update the code to submit messages to the »Meta« Messenger Platform, which is the official API for chat bots on Facebook today.

It looks like the HTTP calls outlined on [1,2] would be the right way to submit messages these days, when doing it with HTTP only. However, I discovered three libraries on PyPI in this space:

• https://pypi.org/project/simple-fbmessenger/
• https://pypi.org/project/messenger-bot-library/
• https://pypi.org/project/messenger-api-python/

I think messenger-api-python is the most prolific one. Maybe @caronc also wants to have a look in order to add a corresponding adapter to Apprise.

With kind regards, Andreas.

[1] https://developers.facebook.com/docs/messenger-platform/send-messages [2] https://developers.facebook.com/docs/messenger-platform/reference/send-api