Expose the deployment strategy values for the policy controller

Prior to this change, the policy controller webhook was not able to have
its deployment strategy modified. If you only deployed a single replica,
it could not perform a rolling update due to the default `maxSurge:
25%` being rounded down to 0.

This change exposes those values, so that the `maxSurge` can be updated
and a single instance can be rolled.

Fixes sigstore#748.

charts/policy-controller/templates/webhook/deployment_webhook.yaml

@@ -12,6 +12,13 @@ spec:
     matchLabels:
       {{- include "policy-controller.selectorLabels" . | nindent 6 }}
       control-plane: {{ template "policy-controller.fullname" . }}-webhook
+
+{{- if .Values.deployment.strategy }}
+  strategy:
+{{ toYaml .Values.deployment.strategy | trim | indent 4 }}
+    {{ if eq .Values.deployment.strategy.type "Recreate" }}rollingUpdate: null{{ end }}
+{{- end }}
+
   template:
     metadata:
       labels: