Clarify usage and scope of different types of tokens

Current we have several tokens (or terms) and it's quite unclear to me what each is intended for:

• basic auth (username and password)

• bear token (header only)

• access token

• upload token (query parameter only)

• signature token (query parameter only)

• app token

• Add more docs to https://gitlab.mpcdf.mpg.de/nomad-lab/nomad-FAIR/-/blob/develop/nomad/app/v1/routers/auth.py?ref_type=heads#L70