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/audit_function.tmpl

@@ -1,4 +1,4 @@
-CREATE OR REPLACE FUNCTION {{.SchemaName}}.{{.FunctionName}}()
+CREATE OR REPLACE FUNCTION {{qual_table_raw .SchemaName .FunctionName}}()
 RETURNS trigger AS
 $body$
 DECLARE
@@ -81,4 +81,4 @@ LANGUAGE plpgsql
 VOLATILE
 SECURITY DEFINER;
 
-COMMENT ON FUNCTION {{.SchemaName}}.{{.FunctionName}}() IS 'Audit trigger function for table {{.SchemaName}}.{{.TableName}}';
+COMMENT ON FUNCTION {{qual_table_raw .SchemaName .FunctionName}}() IS 'Audit trigger function for table {{qual_table_raw .SchemaName .TableName}}';