feat(syncing-server): associating existing items with key systems and shared vaults (#661)

* feat(syncing-server): associating existing items with key systems and shared vaults

* fix(syncing-server): find item query

* feat(syncing-server): add persistence of shared vaults with users and invites

packages/syncing-server/src/Domain/KeySystem/KeySystemAssociationRepositoryInterface.ts

@@ -1,6 +1,9 @@
+import { Uuid } from '@standardnotes/domain-core'
+
 import { KeySystemAssociation } from './KeySystemAssociation'
 
 export interface KeySystemAssociationRepositoryInterface {
   save(keySystem: KeySystemAssociation): Promise<void>
   remove(keySystem: KeySystemAssociation): Promise<void>
+  findByItemUuid(itemUuid: Uuid): Promise<KeySystemAssociation | null>
 }