Move questionnaire (psdm_qs_cli) backend out of happi

[klauer]

Expected Behavior

LCLS-specific questionnaire backend, with its dependency psdm_qs_cli, should not be part of happi.

Current Behavior

LCLS-specific psdm_qs_cli is an included backend in happi: https://github.com/pcdshub/happi/blob/master/happi/backends/qs_db.py

Possible Solution

We have some preliminary ways to add backends externally from happi.
It's not as sophisticated as it should be for general use: https://github.com/pcdshub/happi/blob/master/happi/backends/__init__.py

As we use entrypoints for container classes and already have it as a dependency, it may make sense to go that route.

[hhslepicka]

I just noticed that this one is the same as #130 but much better described. Just looping it in so when this gets closed the other one can go together.