Chart: Allow configuring of deployment strategy

[chris-sanders]

The values for the strategy are not exposed in the chart here.

In particular setting the maxUnavailalbe would be useful since Helm will consider the deployment done early (Ref). When installing a new cluster with the local-pv-provisioner along with other charts this will cause additional charts to be installed before openebs is available. If those charts need volumes the PVC will be stuck in pending because it won't be processed as a request after openebs is done installing.