Support multi-connectors

[sebastianpfischer]

In order to enable the implementation of more complex auxiliaries where several connectors are needed (e.g. 2FA simulations)
we want to extend pykiso to support multiple connectors.

Place to modify:

• https://github.com/eclipse/kiso-testing/blob/master/src/pykiso/interfaces/dt_auxiliary.py to handle one or many connectors
• https://github.com/eclipse/kiso-testing/blob/master/src/pykiso/test_setup/config_registry.py to parse yaml containing one or many connectors declarations
• https://github.com/eclipse/kiso-testing/blob/master/src/pykiso/test_setup/dynamic_loader.py to connect all of them

Acceptance criterias:
AC1: current yaml files still work without any adaption
AC2: parameter available to inform the user he needs to provide one to many aux
AC3: dummy aux or real aux example added
AC4: DoD