Desired Behavior

Very few people actually use dune subst but all the opam files have ["dune" "subst"] {dev} even if they are not using it.
Something to disable that and make dune subst fail if called and disabled would be very helpful.

This idea comes from a comment by @talex5 in #4806 (comment)

Example

$ cat dune-project
(lang dune 3.0)
(enable_subst false)
$ dune subst
Error: The use of "dune subst" has been disabled
$ echo $?
1

It would also remove the ["dune" "subst"] {dev} line from any generated opam file.