need way to set permissions on docker.sock

### Description

I'm running colima on a headless mac build server with multiple users. Per Homebrew advice, I've set up a dedicated user `_homebrew` to manage all Homebrew-installed software.

To run Colima at boot as this user, I have to have a custom LaunchDaemon (the "sudo" brew services plist created isn't correct).

So, the socket is in `~_homebrew/.colima/default/docker.sock`, but the permissions are `srw------- 1 _homebrew staff`, requiring sudo for anyone to run docker commands.

There doesn't seem to be any way to make the socket created with permissions so that I could do the "create a docker group, make the socket group accessible".

I'm able to manually override permissions, but the socket is recreated every time colima starts up and needs to be manually set.

I'd like to be able to explicitly set the socket permissions as a command line option, or at least honor the `Umask` inherited from the LaunchDaemon plist.