Use Plugin API to dynamically define Klaro Consent Services

Problem/Motivation

Seems like services in Klaro are currently defined through config entities. We've solved that similarly in COOKiES, but it has some disadvantages, in cases like:
Dynamically providing services and texts
Dynamically updating services and texts (updates)
Contrib module integration (providing service definitions for their integration)

Drupal has the wonderful Plugin API → functionality and at least in COOKiES ( #3323524: [META] Improve combination of COOKiES submodules and their services through "Drupal Plugins" → ) we came to the conclusion that it might be better to use plugins that return the definiton (e.g. from a configuration entity).

That might also simplify to provide Klaro Consent Service Definitions in contrib modules instead of managing them all in the Klaro module (maybe in a 4.x version). We should focus on the most widely used then, I'd say.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes