feat(queue): move design docs to the EIP

apps/emqx_ds_shared_sub/README.md

@@ -4,20 +4,15 @@ This application makes durable session capable to cooperatively replay messages
 
 # General layout and interaction with session
 
+The general idea is described in the [EIP 0028](https://github.com/emqx/eip/blob/main/active/0028-durable-shared-subscriptions.md).
+
+On the code level, the application is organized in the following way:
+
 ![General layout](docs/images/ds_shared_subs.png)
 
 * The nesting reflects nesting/ownership of entity states.
 * The bold arrow represent the [most complex interaction](https://github.com/emqx/eip/blob/main/active/0028-durable-shared-subscriptions.md#shared-subscription-session-handler), between session-side group subscription state machine (**GroupSM**) and the shared subscription leader (**Leader**).
 
-# GroupSM and Leader communication
-
-The target state of GroupSM and its representation in Leader is `replaying`. That is, when the GroupSM and the Leader agree on the leased streams, Leader sends lease confirmations to the GroupSM, the GroupSM sends iteration updates.
-
-Other states are used to gracefully reassign streams to the GroupSM.
-
-Below is the sequence diagram of the interaction.
-
-![GroupSM and Leader communication](docs/images/groupsm_leader_communication.png)
 
 # Contributing