ADD: Env to change repository's local bare path with docker-gitlab

[whitehander]

Add options to Configuration Parameter.

I want change "scm_git_path_regexp" at config/configuration.yml

[vartistv]

I am looking forward to being able to use this feature.

[jcormier]

If you could create a pull request that would be great. You can search for some of the other config options in the code and match how they were done.