FEATURE: Support designating multiple groups as mods on category (#28655)

Currently, categories support designating only 1 group as a moderation group on the category. This commit removes the one group limitation and makes it possible to designate multiple groups as mods on a category.

Internal topic: t/124648.

spec/serializers/category_serializer_spec.rb

@@ -4,18 +4,19 @@ RSpec.describe CategorySerializer do
   fab!(:user)
   fab!(:admin)
   fab!(:group)
-  fab!(:category) { Fabricate(:category, reviewable_by_group_id: group.id) }
+  fab!(:category)
+  fab!(:category_moderation_group) { Fabricate(:category_moderation_group, category:, group:) }
 
   it "includes the reviewable by group name if enabled" do
     SiteSetting.enable_category_group_moderation = true
     json = described_class.new(category, scope: Guardian.new, root: false).as_json
-    expect(json[:reviewable_by_group_name]).to eq(group.name)
+    expect(json[:moderating_group_ids]).to eq([group.id])
   end
 
   it "doesn't include the reviewable by group name if disabled" do
     SiteSetting.enable_category_group_moderation = false
     json = described_class.new(category, scope: Guardian.new, root: false).as_json
-    expect(json[:reviewable_by_group_name]).to be_blank
+    expect(json[:moderating_group_ids]).to be_blank
   end
 
   it "includes custom fields" do

spec/serializers/post_serializer_spec.rb

@@ -284,12 +284,12 @@ RSpec.describe PostSerializer do
     fab!(:topic)
     fab!(:group_user)
     fab!(:post) { Fabricate(:post, topic: topic) }
-
-    before do
-      SiteSetting.enable_category_group_moderation = true
-      topic.category.update!(reviewable_by_group_id: group_user.group.id)
+    fab!(:category_moderation_group) do
+      Fabricate(:category_moderation_group, category: topic.category, group: group_user.group)
     end
 
+    before { SiteSetting.enable_category_group_moderation = true }
+
     it "does nothing for regular users" do
       expect(serialized_post_for_user(nil)[:group_moderator]).to eq(nil)
     end

spec/serializers/topic_view_serializer_spec.rb

@@ -454,7 +454,10 @@ RSpec.describe TopicViewSerializer do
 
     context "with can_edit" do
       fab!(:group_user)
-      fab!(:category) { Fabricate(:category, reviewable_by_group: group_user.group) }
+      fab!(:category)
+      fab!(:category_moderation_group) do
+        Fabricate(:category_moderation_group, category:, group: group_user.group)
+      end
       fab!(:topic) { Fabricate(:topic, category: category) }
       let(:user) { group_user.user }