Add support for ECA 3

MR!18 implements everything except for the config schema for condition plugins. That's because those plugins are not defined by the eca_commerce module but by the commerce module itself. And there is already config schema for each of them available. ECA Commerce just creates a wrapper around them. To keep maintenance effort manageable, we should try and derive the config schema from their source. Something similar is currently ongoing for eca_tamper at 📌 Add schema definitions for Tamper plugins Active .

This MR gets the 2.1 branch into a state where it supports both ECA 2 and 3, so there is no need for a version jump there. The 2.2.x branch is redundant for now, we just disregard it as we can delete it.

It introduces plugin attributes and full config schema.

jurgenhaas → credited michaellander → .

Crediting @michaellander as he helped me a lot to get the config schema stuff resolved.

Looks great to me thanks!

Thanks for reviewing this @nicxvan