fix(network): allow inspecting pseudo networks

[immanuwell]

refs #3005

nerdctl network ls shows host and none, but nerdctl network inspect host and nerdctl network inspect none still fail. the inspect path asks to allow pseudo networks, but lookup only checked on-disk CNI configs, so these names fell through. kinda awkward.

this returns a small synthetic config for pseudo networks in that lookup path, so inspect can render them fine.

repro:

1. run nerdctl network ls
2. see host and none
3. run nerdctl network inspect host
4. before: fails with no network found matching: host
5. after: returns JSON with "Name": "host"

checks:

• go test ./pkg/netutil -count=1
• go test ./pkg/inspecttypes/dockercompat -count=1
• go test ./cmd/nerdctl/network -run ^ -count=1

[sathiraumesh]

probably can do in a cleaner way i beleive and remove extra function declration and two calls

if name == "host" || name == "none" {
  if !allowPseudoNetwork {
        errs = append(errs, fmt.Errorf("pseudo network not allowed: %s", req))
        continue
    }
    cfg, err := newPseudoNetworkConfig(req)
    if err != nil {
        errs = append(errs, err)
        continue
    }
    list[req] = []*NetworkConfig{cfg}
    continue
}