Added Oasis access restriction via optional white-listing.

gui/src/components/errors.js

nomad/app/flask/api/auth.py

nomad/app/flask/dcat/catalog.py

nomad/app/flask/dcat/datasets.py

nomad/app/main.py

nomad/app/v1/routers/auth.py

nomad/config.py

nomad/infrastructure.py

ops/docker-compose/nomad-oasis/README.md

tests/conftest.py