rm_stm: clear metrics when stopping rm_stm

When `rm_stm` is stopped it should release all used resources including
metrics name. This will allow partition to be recreated if required.

Signed-off-by: Michal Maslanka <michal@redpanda.com>
(cherry picked from commit 4a82177)

src/v/cluster/rm_stm.cc

@@ -1189,6 +1189,7 @@ ss::future<result<kafka_result>> rm_stm::do_replicate(
 ss::future<> rm_stm::stop() {
     auto_abort_timer.cancel();
     _log_stats_timer.cancel();
+    _metrics.clear();
     return raft::state_machine::stop();
 }