Consider making `{project}` placeholder available to `repair-wheel-command`

[arcondello]

Description

I would like to be able to run a script defined in my repo as part of the repair-wheel-command.

Currently, I can hard-code the path for each OS

[[tool.cibuildwheel.overrides]]
select = "*-????linux_*"
inherit.repair-wheel-command = "prepend"
repair-wheel-command = "python /project/scripts/_fix_wheel.py {wheel}"

[[tool.cibuildwheel.overrides]]
select = "*-macosx_*"
inherit.repair-wheel-command = "prepend"
repair-wheel-command = "python ./scripts/_fix_wheel.py {wheel}"

but I'd like to make it more general and more future-proof.

repair-wheel-command = "python {project}/scripts/_fix_wheel.py {wheel}"

I believe this can be accomplished by adding project= to

cibuildwheel/cibuildwheel/platforms/linux.py

Lines 322 to 324 in 3a52416

	repair_command_prepared = prepare_command(
	build_options.repair_command, wheel=built_wheel, dest_dir=repaired_wheel_dir
	)

and similar for the other OS.

If there is agreement that this is OK and there are no other side effects I should be aware of, I would be happy to make the PR.

[henryiii]

I think that sounds useful to me.

[arcondello]

Great! I'll put up a PR soon