--dns* flags are inconsistent with docker

[apostasie]

Description

Discussed in #4378

cc @swagatbora90

Steps to reproduce the issue

docker run -ti --dns="" debian cat /etc/resolv.conf
nerdctl run -ti --dns="" debian cat /etc/resolv.conf

Describe the results you received and expected

Consistent behavior.
Nerdctl should validate the content of explicitly passed --dns* flags.

What version of nerdctl are you using?

main

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

None

Host information

No response

[swagatbora90]

I can send a follow up PR to add DNS validation.