docs: add mariadb gh-ost support

Author: tianzhou

content/docs/introduction/supported-databases.md

@@ -186,4 +186,5 @@ _Schema management is only applicable to RDBMS. If you are looking for a feature
 | PostgreSQL | ✔️                                                                 | ✔️                                                   |                                                                                 |
 | Oracle     | ✔️                                                                 |                                                      |                                                                                 |
 | SQL Server | ✔️                                                                 |                                                      |                                                                                 |
+| MariaDB    |                                                                    |                                                      | ✔️                                                                              |
 | TiDB       | ✔️                                                                 | ✔️                                                   |                                                                                 |