Add 2 questions to FAQ in access and service portfolio section

@aspi.hzb @jandt-desy @s.wagner @andreas.klotz @frust45

As discussed yesterday, here's a proposal to add a question in the FAQ about the different services names.
👉 Question on service names

I took the opportunity to add a question to close #375 (closed).
👉 Question on non-Helmholtz affiliated