wip: test alternate FAB for auth with veda-keycloak

[ividito]

To test, add the following to sm2a-local-config/.env:

KEYCLOAK_BASE_URL=https://keycloak.delta-backend.xyz
KEYCLOAK_REALM=veda
KEYCLOAK_CLIENT_ID=airflow-webserver-fab
KEYCLOAK_CLIENT_SECRET=<get this from keycloak>

The client is configured to allow redirects to http://localhost:8080. Only the airflow-admin role has been configured.

[smohiudd]

I have this branch deployed to SIT: https://sm2a.sit.openveda.cloud/