Add interface to stop synchronization while maintaining realtime sync

What would you like to be added:

Currently, Yorkie has the following synchronization modes:

A. Manual Sync

Manually handle Document synchronization
Do not connect to a stream to receive Document events
Do not add Presence of the Client

await client.attach(doc, { isRealtimeSync: false });

B. Realtime Sync

Automatically handle Document synchronization
- PushPull Mode: Send local changes to other clients and reflect changes from other clients in the local document
- PushOnly Mode: Send local changes to other clients but do not receive changes from other clients, preventing undoing due to remote changes in IME mode
Connect to a stream to receive Document events
Add Client Presence to notify other Clients

await client.attach(doc, {
  initialPresence: { color: 'blue', cursor: { x: 0, y: 0 } },
  isRealtimeSync: true,
});

Refer to

Document Editing: https://github.com/yorkie-team/yorkie/blob/main/design/document-editing.md
PubSub(Event Stream): https://github.com/yorkie-team/yorkie/blob/main/design/pub-sub.md
Synchronization Mode: https://yorkie.dev/docs/js-sdk#changing-synchronization-setting

Additionally, there is a need for a mode where the user can maintain Realtime Sync(register Presence) but neither send nor receive local changes from other clients.

yorkie-team / yorkie

Add interface to stop synchronization while maintaining realtime sync #820