cluster: Reset cloud storage metric...

... in the partition::remove_persistent state. The probe has access to
the global state so it's not safe to keep it after the partition is
stopped and `remove_persistent_state` method is invoked. In cases when
the partition is recreated with different revision id the 'double metric
registration' error could be triggered.

src/v/cluster/partition.cc

@@ -902,6 +902,7 @@ partition::get_cloud_term_last_offset(model::term_id term) const {
 }
 
 ss::future<> partition::remove_persistent_state() {
+    _cloud_storage_probe = nullptr;
     co_await _raft->stm_manager()->remove_local_state();
 }