Run dune build on file save

[nkhlmn]

I have a snippet in my config that will check if I'm in a dune project and if so will run dune build @check and restart the lsp. Could be nice to have that as part of this plugin. Happy to contribute that if you'd like.

[tjdevries]

Hmm, interesting - I think better is running dune build @check -w from the command-line. This is usually what I do. What does this strategy bring compared to that one?