Remove `critical-pod` annotation from Concierge and add `priorityClassName: system-cluster-critical` instead

[cfryanr]

Is your feature request related to a problem? Please describe.

Concierge deployments cause this warning: Warning: spec.template.metadata.annotations[scheduler.alpha.kubernetes.io/critical-pod]: non-functional in v1.16+; use the "priorityClassName" field instead.

Describe the solution you'd like

Remove critical-pod annotation from Concierge and add priorityClassName: system-cluster-critical instead. See this old TODO in the code: https://github.com/vmware-tanzu/pinniped/blob/0651b9a91220bceec8e69c834e506b357dd750fb/deploy/concierge/deployment.yaml#L228-L230

Describe alternatives you've considered

None.

Additional context

Would this prevent deploys on Kube 1.16 and earlier? Would we be okay with that? We don't test against those old unsupported versions, so we're not sure if the Concierge deploys and works on those old versions anyway.