fix(compose): support cgroup_parent and cgroup service fields

[addemod]

Problem

nerdctl compose ignores the cgroup_parent and cgroup service fields, which nerdctl run supports as --cgroup-parent and --cgroupns:

services:
  probe:
    image: alpine
    cgroup_parent: foo.slice

level=warning msg="Ignoring: service probe: [CgroupParent]"

The service still starts, in the default cgroup parent. cgroup: host is dropped the same way and the container keeps a private cgroup namespace. For cgroup_parent that means the container runs outside the resource limits the parent was meant to apply, with only a warning.

Cause

compose-go loads both fields, but the service parser never maps them to run arguments, and neither is in its list of known fields. docs/compose.md lists cgroup_parent as unimplemented.

Fix

Map them in the service parser:

• services.<SERVICE>.cgroup_parent -> --cgroup-parent
• services.<SERVICE>.cgroup -> --cgroupns

Both are added to the known-field list, so the warning goes away. cgroup_parent is removed from the unimplemented list in docs/compose.md.

Verification

Built from this branch and from its merge base with main, and run with nerdctl compose up using the systemd cgroup driver on cgroup v2, containerd 2.2.1 and runc 1.3.3. The cgroup was read from /proc/<pid>/cgroup, and the namespace was compared against the host's /proc/self/ns/cgroup.

service field	unpatched	patched
none	/system.slice/nerdctl-<id>.scope, private ns	same
cgroup_parent: rcs-thirdparty.slice	/system.slice/nerdctl-<id>.scope, Ignoring: [CgroupParent]	/rcs.slice/rcs-thirdparty.slice/nerdctl-<id>.scope
cgroup: host	private ns, Ignoring: [Cgroup]	host ns
cgroup: private	private ns, Ignoring: [Cgroup]	private ns

Test

TestParseCgroup asserts that both fields become --cgroupns=host and --cgroup-parent=foo.slice.

[addemod]

This invalidates PR #5227

[AkihiroSuda]

Please squash the commits

[addemod]

Please squash the commits

@AkihiroSuda Done!

[AkihiroSuda]

Thanks