[docs][hotfix] Configuration 'slot.name' is required in mysql-postgres-tutorial.md (#2764)

This closes #2764.

docs/content/quickstart/mysql-postgres-tutorial.md

@@ -228,7 +228,8 @@ Flink SQL> CREATE TABLE shipments (
    'password' = 'postgres',
    'database-name' = 'postgres',
    'schema-name' = 'public',
-   'table-name' = 'shipments'
+   'table-name' = 'shipments',
+   'slot.name' = 'flink'
  );
 ```