Provide a way to set custom labels on the `Pod`s Eirini deploys

[gcapizzi]

The following fields in eiriniv1.LRP and eiriniv1.Tasl act only as metadata (they get converted to labels):

• GUID
• Version
• Name
• ProcessType
• App/Space/OrgName/GUID

Fields like GUID, Name and Version should be replaced by Kubernetes' ways of identifying objects.

The other fields refer to higher-level concepts Eirini shouldn't be aware of. Instead, we should provide clients with a way to specify their own labels and annotations, which we should then apply to all the resources we create (StatefulSets, Pods). In order to do so, we have two alternatives:

• Add a UserProvidedLabels field (similar to the existing UserProvidedAnnotations
• Let clients set labels and annotations on our CRs, and replicate those