Rename the consumer create service to find or create

The following discussion from !14425 should be addressed:

• @vburton started a discussion: (+9 comments)

  Suggestion: Since we are either finding or creating a consumer, it might make more sense to name this BaseFindOrCreateService, and similar for the other classes being added here:

  • FindOrCreateWithSubscriptionService
  • FindOrCreateWithTrialService

  Along with the create_service_for method being renamed to find_or_create_service_for