Re-introduce `gm_group` table

For mixed-version clusters, as the gm table is created even if
CMQ have already been deprecated

deps/rabbit/app.bzl

@@ -9,6 +9,7 @@ def all_beam_files(name = "all_beam_files"):
     erlang_bytecode(
         name = "behaviours",
         srcs = [
+            "src/gm.erl",
             "src/mc.erl",
             "src/rabbit_backing_queue.erl",
             "src/rabbit_credential_validator.erl",
@@ -266,6 +267,7 @@ def all_test_beam_files(name = "all_test_beam_files"):
         name = "test_behaviours",
         testonly = True,
         srcs = [
+            "src/gm.erl",
             "src/mc.erl",
             "src/rabbit_backing_queue.erl",
             "src/rabbit_credential_validator.erl",
@@ -561,6 +563,7 @@ def all_srcs(name = "all_srcs"):
             "src/background_gc.erl",
             "src/code_server_cache.erl",
             "src/gatherer.erl",
+            "src/gm.erl",
             "src/internal_user.erl",
             "src/lqueue.erl",
             "src/mc.erl",

deps/rabbit/src/gm.erl

@@ -0,0 +1,27 @@
+%% This Source Code Form is subject to the terms of the Mozilla Public
+%% License, v. 2.0. If a copy of the MPL was not distributed with this
+%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
+%%
+%% Copyright (c) 2007-2024 Broadcom. All Rights Reserved. The term “Broadcom” refers to Broadcom Inc. and/or its subsidiaries. All rights reserved.
+%%
+
+-module(gm).
+
+%% Deprecated with CMQ.
+%% This module stays here for mixed-version compatibility, because of
+%% the `gm_group` table. It can be removed once the migration to Khepri
+%% is finalised and Mnesia fully removed.
+
+-export([table_definitions/0]).
+
+-define(GROUP_TABLE, gm_group).
+
+-record(gm_group, { name, version, members }).
+
+-define(TABLE, {?GROUP_TABLE, [{record_name, gm_group},
+                               {attributes, record_info(fields, gm_group)}]}).
+-define(TABLE_MATCH, {match, #gm_group { _ = '_' }}).
+
+table_definitions() ->
+    {Name, Attributes} = ?TABLE,
+    [{Name, [?TABLE_MATCH | Attributes]}].

deps/rabbit/src/rabbit_table.erl

@@ -359,6 +359,7 @@ definitions() ->
 
 mandatory_definitions() ->
     pre_khepri_definitions()
+        ++ gm:table_definitions()
         ++ mirrored_supervisor:table_definitions()
         ++ rabbit_maintenance:table_definitions().