fix(collection): improve duplicate key error reporting on insert

ts/classes.collection.ts

@@ -447,8 +447,22 @@ export class SmartdataCollection<T> {
     }
     
     const saveableObject = await dbDocArg.createSavableObject() as any;
-    const result = await this.mongoDbCollection.insertOne(saveableObject, { session: opts?.session });
-    return result;
+    try {
+      const result = await this.mongoDbCollection.insertOne(saveableObject, { session: opts?.session });
+      return result;
+    } catch (err: any) {
+      const isDuplicateKey = err?.code === 11000 || err?.codeName === 'DuplicateKey';
+      if (isDuplicateKey && dbDocArg.uniqueIndexes && dbDocArg.uniqueIndexes.length > 0) {
+        const identifiableObject = await dbDocArg.createIdentifiableObject();
+        logger.log(
+          'error',
+          `Duplicate key conflict in "${this.collectionName}" on insert. ` +
+          `A document with ${JSON.stringify(identifiableObject)} already exists. ` +
+          `Use getInstance() to retrieve the existing document, or update it via save() on a db-retrieved instance.`
+        );
+      }
+      throw err;
+    }
   }
 
   /**