Core: support optional feature services in FeatureServiceConsumerDependencies

[serbec]

Please introduce the possibility to provide optional feature services for featureServiceDependencies/FeatureServiceConsumerDependencies in the context createFeatureHub. Value: the integrator is able to define optional feature services the integrator depends on.

[unstubbable]

@serbec Do you still need this? Or did you solve this by manually consuming the feature app manager and registry without using the convenience function createFeatureHub?

[serbec]

@unstubbable: I would say - yes, we still need it but the priority is minor. We solved it another way but would like to remove this workaround in the future.