CCM-11228: Update letter schema to include specificationId and groupId

Author: m-houston

internal/datastore/src/types.md

@@ -4,8 +4,10 @@
 ```mermaid
 erDiagram
     Letter {
-        string supplierId "ref: Supplier"
         string id
+        string supplierId "ref: Supplier"
+        string specificationId
+        string groupId
         string url "url"
         string status "enum: PENDING, ACCEPTED, DISPATCHED, FAILED, REJECTED, DELIVERED, CANCELLED"
         string createdAt