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/create_primary_key.tmpl

@@ -6,7 +6,7 @@ BEGIN
       AND table_name = '{{.TableName}}'
       AND constraint_name = '{{.ConstraintName}}'
   ) THEN
-    ALTER TABLE {{quote_ident .SchemaName}}.{{quote_ident .TableName}}
+    ALTER TABLE {{qual_table .SchemaName .TableName}}
       ADD CONSTRAINT {{quote_ident .ConstraintName}} PRIMARY KEY ({{.Columns}});
   END IF;
 END;