Enable PD restore mode during logical restore

## Enhancement

In TiDB restore, it is critical to have tikv processes running with disabled GC for the period of restore.
https://github.com/pingcap/tidb-operator/pull/6267 ensures that, by updating ConfigMaps of tikv. However, that change does not work for TiDB cluster deployments which are spanning multiple K8s clusters.

I propose to use a PD API (see https://github.com/tikv/pd/issues/9638 for details) and enable / disable restore mode in PD before restore starts and after it finished. TiKV could inspect the state of the restore mode on start, and disable GC if restore mode is enabled.