Personal-files Request for the fac Application

@bashfulrobot apologies can I ask you to please make a couple changes (for consistency with previous access to .gitconfig for other snaps) - can you make this a single instance of personal-files and name it just gitconfig like the following:

plugs:
  gitconfig:
    interface: personal-files
    read:
      - $HOME/.gitconfig
      - $HOME/.config/git/config