Enable rootless Podman in gVisor

### Description

Enable running rootless Podman inside a gVisor container.

There are a few blockers to this:
* Networking: Podman sets up for rootless networking using slirp4netns. Rootless networking is WIP in gVisor.
* Storage: fuseoverlayfs disconnect issue
* Networking: in-sandbox rootless networking issues
* virtual nested user namespaces
* virtual cgroup v2 hierarchy

Currently, rootless Podman will work inside a gVisor container if you use the host network and VFS storage driver.

## repro steps
Dockerfile:
```
FROM ubuntu:24.04

# Install Podman and rootless auxiliary utilities
RUN apt-get update && apt-get install -y \
podman \
uidmap \
slirp4netns \
fuse-overlayfs \
curl \
&& rm -rf /var/lib/apt/lists/*

# Configure default rootless registry helper
RUN mkdir -p /etc/containers && \
echo 'unqualified-search-registries = ["docker.io"]' > /etc/containers/registries.conf

# Create a non-root user (e.g., developer) inside the container
RUN useradd -m -s /bin/bash developer && \
echo "developer:100000:65536" >> /etc/subuid && \
echo "developer:100000:65536" >> /etc/subgid

USER developer
WORKDIR /home/developer
```

```
docker run --runtime gvisor-runsc -d --rm \
--cap-add all \
--device /dev/fuse \
--name gvisor-sandbox \
podman-in-gvisor sleep infinity
```

```
docker exec -it -u developer gvisor-sandbox bash

podman info

podman --storage-driver=vfs run --rm -it --network=host alpine echo "Hello from nested Podman!"
```

### Is this feature related to a specific bug?

_No response_

### Do you have a specific solution in mind?

_No response_