add commands to install dune

Author: PizieDust

src/command_api.ml

@@ -154,6 +154,7 @@ module Internal = struct
   let init_opam = unit_handle "init-opam"
   let install_ocaml_dev = unit_handle "install-ocaml-dev"
   let open_utop = unit_handle "open-utop"
+  let install_dune = unit_handle "install-dune"
 end
 
 module Vscode = struct

src/command_api.mli

@@ -55,6 +55,7 @@ module Internal : sig
   val init_opam : (unit, unit) handle
   val install_ocaml_dev : (unit, unit) handle
   val open_utop : (unit, unit) handle
+  val install_dune : (unit, unit) handle
 end
 
 module Vscode : sig