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>

src/v/cluster/rm_stm.cc

@@ -993,6 +993,7 @@ ss::future<> rm_stm::stop() {
     _log_stats_timer.cancel();
     co_await _gate.close();
     co_await reset_producers();
+    _metrics.clear();
     co_await persisted_stm<>::stop();
 }