Add --mount-docker-sock case to support running docker commands

@spacerodent you are the lone docksi man around this week. Mind taking a look at this just to get the ball rolling on MR feedback?

Testing done:

./script.sh --docksi-dry-run
./script.sh --mount-docker-sock
./script.sh --docksi-dry-run --mount-docker-sock
./script.sh --mount-docker-sock --docksi-dry-run
./script.sh --mount-docker-sock --docksi-dry-run --some-foo-argument
./script.sh --some-foo-argument

I still need to test the integration and not just the bash portion.