feat(relations): 🎉 add flatten schema option for output

* Introduce `--flatten-schema` flag to convert, merge, and split commands.
* Modify database writing functions to support flattened schema names.
* Update template functions to handle schema.table naming convention.
* Enhance PostgreSQL writer to utilize flattened schema in generated SQL.
* Update tests to ensure compatibility with new flattening feature.
* Dependencies updated for improved functionality.

pkg/writers/pgsql/templates/set_sequence_value.tmpl

@@ -10,10 +10,10 @@ BEGIN
       AND c.relkind = 'S'
   ) THEN
     SELECT COALESCE(MAX({{quote_ident .ColumnName}}), 0) + 1
-    FROM {{quote_ident .SchemaName}}.{{quote_ident .TableName}}
+    FROM {{qual_table .SchemaName .TableName}}
     INTO m_cnt;
     
-    PERFORM setval('{{quote_ident .SchemaName}}.{{quote_ident .SequenceName}}'::regclass, m_cnt);
+    PERFORM setval('{{qual_table_raw .SchemaName .SequenceName}}'::regclass, m_cnt);
   END IF;
 END;
 $$;