Podman: automatic `--userns=keep-id` breaks containers using host networking

I'm facing an issue when using podman and `--network=host` combination:

## Environment

- `@devcontainers/cli`: 0.88.0
- Podman client/server: 5.7.1
- Host: WSL2
- Podman server: rootful

## Problem

For Podman on Linux and a non-root `remoteUser`, Dev Containers automatically adds:

```text
--security-opt label=disable --userns=keep-id
```

See https://github.com/devcontainers/cli/issues/1004 and https://github.com/microsoft/vscode-remote-release/issues/10399.

When the configuration also requires `--network=host`, the container fails to start.

## Minimal underlying reproducer

This fails:

```sh
podman run --rm \
--network=host \
--userns=keep-id \
docker.io/library/alpine:3.20 \
true
```

Error:

```text
crun: mount `sysfs` to `sys`: Operation not permitted: OCI permission denied
```

Without `--userns=keep-id`, it succeeds:

```sh
podman run --rm \
--network=host \
docker.io/library/alpine:3.20 \
true
```

The CLI-generated `podman run` command contains both:

```text
--userns=keep-id --network=host
```

The automatic argument is added in:

```text
src/spec-node/singleContainer.ts
getPodmanArgs()
```

## Expected behavior

Users must be able to prevent the CLI from adding `--userns=keep-id`.

## Possible fixes

No one is perfect I'm afraid.

1. Do not add `--userns=keep-id` when `--network=host` is present.
2. Add a setting or CLI option to disable automatic Podman arguments.
3. Respect an explicit `--userns=...` in `runArgs` and do not add `--userns=keep-id`.
4. Make automatic `--userns=keep-id` opt-in instead of unconditional for non-root users.

Big thanks.

Start in src/spec-node/singleContainer.ts at getPodmanArgs(), then compare how runArgs and --network=host are incorporated into the generated Podman command. Use the Alpine reproducer from the issue to verify the conflicting arguments, and confirm that an explicit user choice can prevent the failing automatic combination.

Scritto dal modello di indicizzazione a partire dal testo della issue.