Per docker image changes, this serves as an alternative entrypoint for
performing initial pubkey configuration.

Signed-off-by: Malfurious <m@lfurio.us>

Building from debian:latest will make for a smaller image, a faster
build, and will make the image more accessible to a wider variety of
platforms.

The effort started by 19e7dc8932c is expanded upon such that the image
cleanly bakes in all static config files into the image - ie. the entire
hosting user's home directory, except for the repositories directory.
This removal of config management from the gitolite-admin repo is part
of the reason why it is being decoupled from this repo.

The gitolite image will now never utilize a user pubkey during build.
Instead, it can be invoked with an alternative entrypoint to
interactively configure a new install.

Signed-off-by: Malfurious <m@lfurio.us>