feat: user to user message model. (#649)

Co-authored-by: Mo <[email protected]>

packages/syncing-server/src/Domain/Message/MessageRepositoryInterface.ts

@@ -0,0 +1,9 @@
+import { Uuid } from '@standardnotes/domain-core'
+
+import { Message } from './Message'
+
+export interface MessageRepositoryInterface {
+  findByUuid: (uuid: Uuid) => Promise<Message | null>
+  save(message: Message): Promise<void>
+  remove(message: Message): Promise<void>
+}