podman: new option --preserve-fd

add a new option --preserve-fd that allows to specify a list of FDs to
pass down to the container.

It is similar to --preserve-fds but it allows to specify a list of FDs
instead of the maximum FD number to preserve.

--preserve-fd and --preserve-fds are mutually exclusive.

It requires crun since runc would complain if any fd below
--preserve-fds is not preserved.

Closes: https://github.com/containers/podman/issues/20844

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/specgen/generate/container_create.go

@@ -355,6 +355,10 @@ func createContainerOptions(rt *libpod.Runtime, s *specgen.SpecGenerator, pod *l
 		options = append(options, libpod.WithPreserveFDs(s.PreserveFDs))
 	}
 
+	if s.PreserveFD != nil {
+		options = append(options, libpod.WithPreserveFD(s.PreserveFD))
+	}
+
 	if s.Stdin {
 		options = append(options, libpod.WithStdin())
 	}