It should be possible to run integration tests against docker without sudo

### Description

Currently, `-exec sudo` is required when targeting docker for integration tests.

It should be possible to test without that.

There are currently issues preventing it - most of them around `systemctl` w/o `--user`, but also some tests assuming you can manipulate from the host any filesystem resource controlled but the daemon.

Or if this is not desirable, we should check and fail immediately if not root.

### Steps to reproduce the issue

_No response_

### Describe the results you received and expected

na

### What version of nerdctl are you using?

main

### Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

### Host information

_No response_