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/base_constraint.tmpl

@@ -1,6 +1,6 @@
 {{/* Base constraint template */}}
 {{- define "constraint_base" -}}
-ALTER TABLE {{.SchemaName}}.{{.TableName}}
+ALTER TABLE {{qual_table_raw .SchemaName .TableName}}
   ADD CONSTRAINT {{.ConstraintName}}
   {{block "constraint_definition" .}}{{end}};
 {{- end -}}
@@ -15,7 +15,7 @@ BEGIN
           AND table_name = '{{.TableName}}'
           AND constraint_name = '{{.ConstraintName}}'
     ) THEN
-        ALTER TABLE {{.SchemaName}}.{{.TableName}}
+        ALTER TABLE {{qual_table_raw .SchemaName .TableName}}
           DROP CONSTRAINT {{.ConstraintName}};
     END IF;
 END;