Add @damiendoligez `sorttest` (idle domain GC) benchmark

[fabbing]

This PR adds @damiendoligez sorttest which was used to validate changes to fix the idle domain issue: https://github.com/ocaml/ocaml/issues/11589 and https://github.com/ocaml/ocaml/issues/12042.

Changes have been made to trigger global GC major slices and to GC work accounting: https://github.com/ocaml/ocaml/pull/11903.

Two runs are configured:

• 'senquential' the nomimal one, with only one domain
• 'idle-domain', where an additional domain is spwaned and must cooperate on the GC tasks

Under the orun wrapper, top_heap_words, heap_words, major_words, minor_collections and major_collections are relevant information to look at.