Co-authored-by: Prometheus Operator Bot <prom-op-bot@users.noreply.github.com>

Co-authored-by: Prometheus Operator Bot <prom-op-bot@users.noreply.github.com>

Updates Prometheus Adapater image to official image documented in
kubernetes-sigs/prometheus-adapter/README.md

Signed-off-by: Damien Grisonnet <dgrisonn@redhat.com>

Adding a PodDisruptionBudget to prometheus-adapter ensure that at least
one replica of the adapter is always available. This make sure that even
during disruption the aggregated API is available and thus does not
impact the availability of the apiserver.

Signed-off-by: Damien Grisonnet <dgrisonn@redhat.com>

Starting with Kubernetes 1.6 `kubectl apply` works for TPRs so we can
start using it, therefore using multiple files is no issue.