POST role-binding API - spec

• Should implement the API as documented by the spec
• API should be consistent with other RBAC V2 APIs
• Shared in the team-mgmt-fabric channel and reviewed by architects and leads
• Have to consider this: https://issues.redhat.com/browse/RHCLOUD-37863
  • For implementing Serializable isolation, we introduced an @atomic decorator and a mixin to apply this across all APIs in a given namespace
  • Use the same pattern. The mixin may need to be updated to work for batch delete method
  • Something to note is that the decorator for an atomic transaction should be in the service layer method as well as the view.
• Should follow hexagonal architecture principles. The attached diagram is a good reference of how to organize concerns between layers. Please use the CreateRole PR as a reference. 
• Tests should be implemented for each layer.