Implement plugins from other social posting modules

Problem/Motivation

Social post controller module provides a SocialPlatform plugin type, which among other things, defines an abstract method to invoke the post method from any modules implementing the plugin.

It would be good at some point for issues to be created, and code submitted to the following modules:

• Social post facebook
• Social post twitter
• Activitypub

and more. More or less, just putting this issue here as a reminder that this plugin architecture is the way we are moving, and that we need to implement it when ready to start using this module.