Feature: add function based option to ignore services

[Mairu]

Is your feature request related to a problem? Please describe. Sometimes there are services that should not be added to the swagger specs, f.e. services added by feathers-distributed. See a detailed case and workaround solution in https://github.com/feathersjs-ecosystem/feathers-swagger/issues/191

Describe the solution you'd like There should be an option additional to tags and paths, to ignore services based on a function that gets the service and return true or false.