Docker support

[kevinholtkamp]

Is your feature request related to a problem? Please describe.
I want to use Pi-Hole when outside of the home by using private DNS, but I am running it inside of docker

Describe the solution you'd like
A docker image for Pi-Hole that contains this repo

Describe alternatives you've considered
Manually installing this in my container, but that would be overwritten in an update or when migrating.

Additional context
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