Invoke flogo activity as a rule action

[rameshpolishetti]

Current behavior:
Currently, rule action is a Go function.

Expected behavior:
Able to configure a flogo activity as a rule action, so that it gets invoked when the rule fires.

What is the motivation / use case for changing the behavior?
This allows rules application to send events/messages to external applications by leveraging various flogo activities readily available (ex: rest, kafka, etc...)

Additional information you deem important (e.g. I need this tomorrow):

[mellistibco]

@skothari-tibco is working on an activity to invoke an action. Perhaps this or something similar can be used. For invoking actions in an async manner, that is something we can do with a flogo channel...