Integrate docker-helper functionality into cht-conf

[eljhkrr]

Is your feature request related to a problem? Please describe.

Docker helper scripts are hosted on the cht-core repository here:
https://github.com/medic/cht-core/tree/master/scripts/docker-helper-4.x

Usage is documented here:
https://docs.communityhealthtoolkit.org/apps/guides/hosting/4.x/app-developer/

Without prior knowledge of its existence it's easy to stumble around trying to setup a local CHT environment to experiment with.

Describe the solution you'd like

Including docker-helper functionality within cht-conf would make it convenient to use and easy to discover.

Describe alternatives you've considered

CHT developer environment setup is the only alternative available but is needlessly complicated for users not interested in contributing to CHT.