update for sr3 configuration and callback

[RousseauLambertLP]

update for sr3 configuration and callback

• replaced message.py and file_.py by event_plugin.py for the callback functions. Both cases are handled in a single file.
• event_plugin.py updated for callback instead of the previous plugin
• added exchange xpublic to all configuration
• updated the env var to point to the class in the callback (sr3) instead of the event file (sr2)
• reordered amqps configuration file for consistency

[Dukestep]

We've run into an issue where the approach of having the after_work and after_accept methods in a single Event class will not work. There is no way to specify which method to call via the sr3 subscriber which triggers the callback.

Reid at SSC suggests we split them back out into individual files.

Peter also suggested adding our own option and using if statements to control which methods get run: https://metpx.github.io/sarracenia/api-documentation.html#config:~:text=with%20queue%20bindings.-,add_option(,-option%2C%20kind.

The following example is handy to: https://github.com/MetPX/sarracenia/blob/development/sarracenia/flowcb/send/email.py