[REF] mail: move discuss.channel/legacy_insert to discuss folder

Part of task-3265211

Part-of: odoo/odoo#128593

addons/mail/static/src/core/common/messaging_service.js

@@ -166,14 +166,6 @@ export class Messaging {
                 case "mail.record/insert":
                     this._handleNotificationRecordInsert(notif);
                     break;
-                case "discuss.channel/legacy_insert":
-                    this.threadService.insert({
-                        id: notif.payload.channel.id,
-                        model: "discuss.channel",
-                        type: notif.payload.channel.channel_type,
-                        ...notif.payload,
-                    });
-                    break;
                 case "discuss.channel/transient_message": {
                     const channel =
                         this.store.threads[createLocalId("discuss.channel", notif.payload.res_id)];

addons/mail/static/src/discuss/core/common/discuss_core_common_service.js

@@ -61,6 +61,14 @@ export class DiscussCoreCommon {
                     { type: "info" }
                 );
             });
+            this.busService.subscribe("discuss.channel/legacy_insert", (payload) => {
+                this.threadService.insert({
+                    id: payload.channel.id,
+                    model: "discuss.channel",
+                    type: payload.channel.channel_type,
+                    ...payload,
+                });
+            });
             this.busService.addEventListener("notification", ({ detail: notifications }) => {
                 // Do not handle new message notification if the channel was just left. This issue
                 // occurs because the "discuss.channel/leave" and the "discuss.channel/new_message"