Do real basic auth

[soxofaan]

with #168 we now have a basic config system that also can hold some secrets like real basic auth (instead of the silly basic implementation we have now)

[soxofaan]

related to (and maybe even overruling) #90

[soxofaan]

Another possibility: do basic auth through OIDC password grant behind the scenes (for example using VITO keycloak for the Terrascope back-end). This would allow to use standard tools (Keycloak) to create/manage users, instead of a DIY solution through config

[soxofaan]

(edited: accidentally commented and committed under this ticket, while that should have been under #193)

[soxofaan]

FYI, basic auth is not practically non-functional on terrascope backend as it raises a "unsufficient credits" error

curl -i -X POST -H 'Content-Type: application/json' -H 'Authorization: Bearer basic//abc123==' --data '{"process":{"process_graph":{}}}' https://openeo-dev.vito.be/openeo/1.1/result

HTTP/2 401 
content-type: application/json
date: Wed, 25 Oct 2023 13:35:13 GMT
content-length: 188
strict-transport-security: max-age=31536000; includeSubDomains

{"message":"You do not have sufficient credits to perform this request. Please visit https://portal.terrascope.be/pages/pricing to find more information on how to buy additional credits."}