Switching Boskos to deployment, as well as removing persistent volume

[chaodaiG]

This change is to make our Boskos deployment consistent with upstream, almost a mirror of kubernetes/test-infra#13594

Also copied from the PR above:

kubectl delete -n test-pods statefulset boskos
# wait for boskos-0 pod to be gone in test-pods ns
kubectl delete -n test-pods pv boskos-storage
kubectl apply -f ci/prow/deployments/boskos_deployment.yaml

Part of: #1533

/cc @yt3liu
/cc @sebastienvas

[knative-prow-robot]

@chaodaiG: GitHub didn't allow me to request PR reviews from the following users: sebastienvas.

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In response to this:

This change is to make our Boskos deployment consistent with upstream, almost a mirror of kubernetes/test-infra#13594

Part of: #1533

/cc @yt3liu
/cc @sebastienvas

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[chaodaiG]

/hold
So that this PR doesn't get merged at a wrong time

[yt3liu]

/lgtm

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: adrcunha, chaodaiG

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[chaodaiG]

/hold cancel