Allow to set Tolerations via spec.deployments.tolerations - #747

Part of #5

This patch adds `spec.deployments.tolerations` to set tolerations on
each deployment.

For example, when the following CR is created,
```
apiVersion: operator.knative.dev/v1alpha1
kind: KnativeServing
metadata:
  name: ks
  namespace: knative-serving
spec:
  high-availability:
    replicas: 1

  deployments:
  - name: webhook
    tolerations:
    - effect: NoSchedule
      key: node-type
      operator: Equal
      value: production
```

The webhook deployment has `spec.template.spec.tolerations`.

```
$ kubectl get deploy webhook -o jsonpath={.spec.template.spec.tolerations}
[{"effect":"NoSchedule","key":"node-type","operator":"Equal","value":"production"}]
```