Create mssql testcontainer backed webapplicationfactory for service tests

[adrianhall]

There is a set of client tests that use a live service. Switch this to use a mssql backed webapplicationfactory so that we don't need a live "real" server to run the tests.

[adrianhall]

There was precisely one sample server test and it wasn't even that important!

We should have more, but that is a topic for another day.