NUMTRACKER_AUTH_HOST variable is used for both authn and authz #291

When starting the server, it is used to specify the authZ host used to check permissions. When running the client, it is the authN provider where user tokens should be sourced.

Running the client from docker compose, eg to configure beamlines for tests, uses the authZ host for authN and falls over.

It is probably sensible to introduce NUMTRACKER_AUTHN_HOST and NUMTRACKER_AUTHZ_HOST variables to differentiate them. If we can alias the current NUMTRACKER_AUTH_HOST variable it would reduce the configuration changes required in deployments.

NB, if/when this is changed, the DLS module file should be updated to use the new variables when running module load numtracker[/staging]