community/dune: add -configurator subpackage

Hopefully the changes are not too drastic.

I had to replace make release with ./dune.exe build (which is what the Makefile calls anyway), because I get error messages while installing dune-configurator if I don't build dune and dune-configurator together.

An alternative would be to build dune, install it in package(), and then cleanup $builddir before building and installing dune-configurator separately in the configurator() subpackage function, but I did that once, and was told that it is better to do all the building in build().

Unfortunately, as the dune-configurator subpackage contains OCaml modules, unlike dune which is only a binary, the textrels problem is encountered on 32-bit platforms, and options="textrels" has to be used (I tried applying it only to the subpackage, but that didn't work).

If the changes are too much for v3.16, then waiting until after it is released is alright too.