Add missing 'label' for conditions in config schema

I pushed a fix to the MR branch.

This is not a bug, we haven't had labels on conditions since the very beginning, but I can see that it would be nice to have them as well like for events and actions.

However, just adding a schema item is not sufficient here. This is triggered by the request coming from eca_cm, but that modeller is not using any of the APIs that ECA provides for modellers to read and write models. As we do not recommend the usage of the classic modeller, we can only add new features into ECA that come through the proper API.

In the case of conditions labels, this process needs to start by looking into \Drupal\eca\Entity\Eca::addCondition which modellers are supposed to be calling when they want to add a condition to a model while saving it. Currently, this method doesn't accept a label, which should be changed, as well as all downstream methods as well.

While being on it, we should then also enhance the debugging/logging calls, so that they also take the condition labels into account.

Re-basing this on the 2.0.x branch, since this is where new feature will be added.

Not a beta blocker, marked that by mistake.

@ergonlogic are you still up for this challenge?