Feature Request: Add advanced selector to actions

[nik-lampe]

I want to target a german and an english audience. I distinguish these by a language parameter on signup.

It would be nice to be able to trigger certain actions, in my case different double opt-in requests, based on the parameters like in the campaign setup.

Maybe this could be also related to #49, so that there is not just a config in the settings, but maybe custom customer facing pages based on certain contact parameters. But I guess this would be even more effort.

[nik-lampe]

As a workaround I will use a different event based on the contacts language, so subscribed_german and subscribed_english. But it still would be nice to have.

If i find some time, I will also look into the code and try to help

[nik-lampe]

I am currently implementing this feature in my own fork. If there's interest, I'd be happy to submit a pull request so we can refine the details together.

Let me know if you'd like me to proceed with the PR.

[driaug]

All contributions are very much welcomed!