fix: honor --workdir in compose run

[immanuwell]

Fix nerdctl compose run --workdir so it actually sets the container cwd.

Right now compose run --workdir /tmp writes /tmp into the project working dir, not the service working dir. So pwd still does not run from /tmp, and relative host paths can get a bit weird too.

Repro

1. Create a compose file with:

services:
  app:
    image: alpine
    entrypoint:
      - pwd

2. Run nerdctl compose run --workdir /tmp app
3. Before this patch, it does not print /tmp

This patch writes ro.WorkDir to targetSvc.WorkingDir, which is what serviceparser turns into -w=.... Added a regression test too, pretty small and to the point.

[AkihiroSuda]

Thanks