Add HTTP basic auth

So that a username/password combination can be provided by environment variables to the service. All endpoints (except service info?) should be under auth.

Close with tests that demonstrate the server running under basic auth using a client that can use the username/pass combination.

For examples of making pluggable auth with connexion see dos_connect:

https://github.com/ohsu-comp-bio/dos_connect/blob/master/dos_connect/server/basic_authorizer.py

Start by reviewing the service's endpoint and server setup, then compare the pluggable Connexion auth example in dos_connect/server/basic_authorizer.py. Add tests that run the server with credentials supplied through environment variables and authenticate a client against protected endpoints, while confirming the service-info exception if retained.

Written by the indexing model from the issue text.