Alternative authentication for onboarding

[achmelo]

Is your feature request related to a problem? Please describe.
API ML requires x509 authentication for onboarding. This brings additional complexity for users trying to onboard APIs.

Describe the solution you'd like
Provide alternative way of authentication for service registration.

Describe alternatives you've considered
Improve service administration in the API ML.

[balhar-jakub]

When discussing this topic, we should keep in mind the option of onboarding the services on the API Mediation Layer side e.g. by System Programmer within UI.

The current onboarding depends on the System Programmer knowledge and configuration nevertheless and having the configuration in the API Mediation Layer may be a simpler way to solve the issue overall.