Introduce parameters object for AbstractAddStepHandler

Similar to WFCORE-767, the constructors for AbstractAddStepHandler are getting quite convoluted.

Talking with Brian, we think the existing set of constructors are fine. They cover all the common cases, but make it hard to add more parameters. So we will introduce a Parameters object variant there as well, to support what is already there and to make adding new parameters easier as we go along.