Missing docker agent label field.

As I understand it, you can specify a docker agent like below with a label. This option/field is however not available in the blue ocean plugin, as can be seen in the attached images. Same goes for the dockerfile agent.
agent {
docker

{ image 'maven:3-alpine' label 'my-defined-label' args '-v /tmp:/tmp' }

}
from: https://jenkins.io/doc/book/pipeline/syntax/