glom: provide bin dir of postgresql

By default `pg_config --bindir` is executed during configure phase to
get the bin directory containing all the postgres executables used by
glom.

This seems wrong given that the same postgresql_15 package will be
executed on build and on the final host platform which is not
necessarily the same. To avoid that, specify the bin dir manually via
the corresponding configure option.

pkgs/applications/misc/glom/default.nix

···
     python3.pkgs.pygobject3
     gtksourceview
     gtksourceviewmm
-    postgresql_15 # for pg_config
+    postgresql_15 # for postgresql utils
   ];
 
   enableParallelBuilding = true;
···
 
   configureFlags = [
     "--with-boost-python=boost_python${lib.versions.major python3.version}${lib.versions.minor python3.version}"
+    "--with-postgres-utils=${lib.getBin postgresql_15}/bin"
   ];
 
   makeFlags = [