Allow users to customize exclusiveness by selecting which pods the job should not co-exist with

[ahg-g]

Currently the exclusive option enforces exclusiveness again other jobs, we can make that as a default and allow users to customize this choice by adding a labelSelector to the api.

The labelSelector would be merged with the one used in the antiAffinity term that excludes the job itself.

podSelector *metav1.LabelSelector `json:"podSelector,omitempty"`

defaults to:

metav1.LabelSelector{MatchExpressions: []metav1.LabelSelectorRequirement{{
			Key:      jobset.JobNameKey,
			Operator: metav1.LabelSelectorOpExists,
}

[danielvegamyhre]

/assign

[ahg-g]

superseded by #75