Add `astro dev clean` to clean up Docker artifacts

[bounlu]

Running astro dev restart leaves behind dangling Docker images i.e. <none> and a growing Docker build history. It is desirable to clean up them from time to time within astro cli. Particularly the below two commands will be useful for clean up:

docker image prune --force
docker buildx history rm --all

I suggest to add a handy function to astro as below to achieve this:

astro dev clean