Add support for token-based access to the API

[ka7eh]

Users should be able to sign up, create tokens, and use that token to access the API.

We don't need to change any endpoint for now to make the token mandatory, but we can have a dummy endpoint to test the token support. The token support should be added to endpoints as a FastAPI injectable dependency.

The reason for this is to see (and maybe control) how much data is being fetched from the API by different users and services.

Update: we can enable the token support for endpoints that return all records, e.g. /species/all.