docs: prepare to deprecate broker.shared_dispatch_ack_enabled

apps/emqx/i18n/emqx_schema_i18n.conf

@@ -1078,11 +1078,13 @@ Supported configurations are the following:
 
     broker_shared_dispatch_ack_enabled {
         desc {
-            en: """Enable/disable shared dispatch acknowledgement for QoS 1 and QoS 2 messages.
+            en: """Deprecated, will be removed in 5.1.
+Enable/disable shared dispatch acknowledgement for QoS 1 and QoS 2 messages.
 This should allow messages to be dispatched to a different subscriber in the group in case the picked (based on `shared_subscription_strategy`) subscriber is offline.
 """
 
-            zh: """启用/禁用 QoS 1 和 QoS 2 消息的共享派发确认。
+            zh: """该配置项已废弃，会在 5.1 中移除。
+启用/禁用 QoS 1 和 QoS 2 消息的共享派发确认。
 开启后，允许将消息从未及时回复 ACK 的订阅者 （例如，客户端离线）重新派发给另外一个订阅者。
 """
         }

apps/emqx/src/emqx_schema.erl

@@ -1198,6 +1198,10 @@ fields("broker") ->
             sc(
                 boolean(),
                 #{
+                    %% TODO: deprecated => {since, "5.1.0"}
+                    %% in favor of session message re-dispatch at termination
+                    %% we will stop supporting dispatch acks for shared
+                    %% subscriptions.
                     default => false,
                     desc => ?DESC(broker_shared_dispatch_ack_enabled)
                 }