dockerContainer should be pinned to a label (group) of hosts

### What feature do you want to see added?

`pipeline {
agent {
dockerContainer {
image "ubuntu:jammy-20250530"
label "linux"
}
}
....
}`

Invalid config option "label" for agent type "dockerContainer". Valid config options are [image, connector, credentialsId, dockerHost, remoteFs] @ line 5, column 13.

In a setup where jenkins' can dispatch jobs on a mix of nodes, either windows, linux, etc. The ubuntu images only run on hosts which is backed by Linux & dockerd.

Obviously, using the "label" => "linux" isn't supported. Can I be assured that the dockerContainer would run on any of my Linux hosts in this setup?

### Upstream changes

_No response_

### Are you interested in contributing this feature?

_No response_