Add notion of LabelKind to support passing schema info to adapters.
Add notion of LabelKind to support passing schema info to adapters.

rkpagadala/mixer,mandarjog/mixer,istio/old_mixer_repo,guptasu/mixer,ZackButcher/mixer,jmuk/mixer,istio/old_mixer_repo,xiaolanz/mixer,mandarjog/mixer,rkpagadala/mixer,guptasu/mixer,guptasu/mixer,xiaolanz/mixer,douglas-reid/mixer,mandarjog/mixer,jmuk/mixer,rkpagadala/mixer,douglas-reid/mixer,jmuk/mixer,ZackButcher/mixer,xiaolanz/mixer,istio/old_mixer_repo,ZackButcher/mixer,douglas-reid/mixer