Support for `--bare` git repos

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

Using git to manage configuration dot files in ones home dir is tricky when trying to version control files directly in one's $HOME dir. This has lead to a common idiom where people use a bare repo for their dot files, e.g. the first 3 matches from a google search:

• https://www.atlassian.com/git/tutorials/dotfiles
• https://mjones44.medium.com/storing-dotfiles-in-a-git-repository-53f765c0005d
• https://harfangk.github.io/2016/09/18/manage-dotfiles-with-a-git-bare-repository.html

The problem with this is that one has to manually specify the repo path when peforming git actions, e.g.

git --git-dir=$HOME/.dotfiles --work-tree=$HOME add /some/file.py

Which is usally handled by an alias:

alias config="git --git-dir=$HOME/.dotfiles --work-tree=$HOME"

I love Neogit and would like to be able to use it with my dot files, but as far as I tell, it only works by using your cwd, there is not way to specify which repo to use.

Describe the solution you'd like

An option to dynamically specify the repo to use with Neogit, so one use Neogit as it is currently with the cwd, but also be able to create mappings to open Neogit on a specified repo outside of the cwd (related to #305 ), or oin a bare repo.

Describe alternatives you've considered
Crying

Start by tracing Neogit's current cwd-based repository selection and review the related #305 discussion; the payload names no files or tests. Done means Neogit still works from the cwd while mappings can select another repository, including a bare dot-files repository.