[2SP] Integrate RBAC into GNU Radio 4 message handling

[RalphSteinhagen]

• Add message dicarding filters based on a user-defined predicate.
• Implement tests to discard/approve messages based on user roles
• the RBAC checks should be done only on the OpenCMW in/out side.. Once the messages are received there should be no further RBAC checks in GR4. I.e. shift this to the upper point.