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/migration_writer.go

@@ -31,7 +31,7 @@ type MigrationWriter struct {
 
 // NewMigrationWriter creates a new templated migration writer
 func NewMigrationWriter(options *writers.WriterOptions) (*MigrationWriter, error) {
-	executor, err := NewTemplateExecutor()
+	executor, err := NewTemplateExecutor(options.FlattenSchema)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create template executor: %w", err)
 	}