Dynamic URLs in the Feeds tab of the Form editor

[StanZGenchev]

Is your feature request related to a problem? Please describe.
Sometimes, the URL for the feed is not static. We need to have a way to interpolate variables in the URL and possibly call a function that will handle the response data.

Describe the solution you'd like
The ability to interpolate variables in the URL string and specify a function name that will be called after the data is received.