support to tweak resource limits and requests for knative deployments

[nak3]

limits and requests are defined like https://github.com/knative/serving-operator/blob/master/cmd/manager/kodata/knative-serving/0.8.0.yaml#L752-L758, but they are not configurable.

E.g - If we changed resources.limits by kubectl edit deployment autoscaler -n knative-serving, it is reverted with same reason of #160.

[aliok]

One way of supporting this would be #277