rabbit_db: Skip reset if the node is already virgin

[Why]
If we run `reset` again on an already virgin node, it will take
decisions based on the wrong state. In particular, the previous use of
Khepri or Mnesia is lost with the first reset. Therefore, the second
reset wolud delete non-Khepri related files that belong to the
coordination Ra system.

This is particularily problematic with the previously documented way of
joining two nodes using the CLI:

    rabbitmqctl stop_app
    rabbitmqctl reset
    rabbitmqctl join_cluster $REMOTE_NODE
    rabbitmqctl start_app

Indeed, `join_cluster` implies a reset. If the admin already reset the
node as documented, `join_cluster` implied reset would delete too many
files, breaking Khepri after the join if Khepri is used by the remote
node.

[How]
In `rabbit_db:reset/0`, we skip the reset if the node is already virgin.

Fixes #14748.

Author: dumbbell

deps/rabbit/src/rabbit_db.erl

@@ -128,11 +128,21 @@ clear_init_finished() ->
 %% @doc Resets the database and the node.
 
 reset() ->
-    ok = case rabbit_khepri:is_enabled() of
-             true  -> reset_using_khepri();
-             false -> reset_using_mnesia()
-         end,
-    post_reset().
+    IsVirgin = is_virgin_node(),
+    case IsVirgin of
+        true ->
+            ?LOG_INFO(
+               "DB: skipping resetting; node already virgin",
+               #{domain => ?RMQLOG_DOMAIN_DB}),
+            ok;
+        false ->
+            IsKhepriEnabled = rabbit_khepri:is_enabled(),
+            ok = case IsKhepriEnabled of
+                     true  -> reset_using_khepri();
+                     false -> reset_using_mnesia()
+                 end,
+            post_reset()
+    end.
 
 reset_using_mnesia() ->
     ?LOG_INFO(