Always generate the version through git when possible, and encode that within
the binaries so that `catala --version` does'nt give misleading information.
Previously we used dune's builtin functionality, but that resorts to a hack at
install time which is unpleasant and doesn't work with our use of `opam
install`.
The cost is a re-linking of catala_utils and the binaries upon git commit, which
is hardly noticeable.
We have an obvious limitation: static builds won't support plugins. We
could resort to the classic method and do normal builds but on an old
distrib to dodge compatibility issues.
That would still be compatible with statically linking the more specific
libs, like e.g. z3.
