FIX(app): use POSTGRES_PASSWORD from Vault

- Change PASSWORD to POSTGRES_PASSWORD
- Use correct Vault key name

deploy/k8s/overlays/prod/externalsecret.yaml

@@ -54,5 +54,5 @@ spec:
     - secretKey: password
       remoteRef:
         key: databases/postgresql
-        property: PASSWORD
+        property: POSTGRES_PASSWORD