rehearse: enable auto rehearsal of specific jobs with annotation

[dhiller]

Having the new skip-review label enables us to get PRs merged automatically, however, to improve this by avoiding possibly breaking image changes we could add an annotation that holds job names that are automatically triggered when the PR is created.

Example:

In case a job is changed which contains an annotation entry like so

          annotations:
            rehearsal.auto: pull-kubevirt-e2e-k8s-1.31-sig-compute,pull-kubevirt-e2e-kind-sriov
            rehearsal.required: true

a rehearsal of those jobs could be kicked off - additionally those rehearsals would be marked as required (TODO: need to check whether that is possible)

          /rehearse pull-kubevirt-e2e-k8s-1.31-sig-compute
		  /rehearse pull-kubevirt-e2e-kind-sriov

Originally posted by @dhiller in #3778 (comment)

[dhiller]

/kind enhancement
/area automation
/priority backlog

@brianmcarey FYI