Create ADR for Authentication handling

[maximiliantech]

What would you like to be added:
Create an ADR that covers the Authentication issue currently exists for the metrics-operator.

Why is this needed:

[reshnm]

I think before creating an ADR we should gather requirements for different authentication methods and protocols.
We it is known, what kind of endoints shall be supported, then we can decide what we already support and what is missing.
The problem is, there is no standard in terms of transport protocols and authentication in the open telemetry specification.