executor REST API: use "dut(s)" in endpoints instead of "machine(s)" and needed changes to use this everywhere
Update endpoints to use /dut(s)/ in adition to /machine(s)/ to follow the renaming in other parts of the executor.
The current endpoints with /machine(s)/ will be kept around for some time to ease the transition.
Many changes to make the code use the new endpoints.
Fixes: https://gitlab.freedesktop.org/mupuf/valve-infra/-/issues/135