dolt doesn't support `source` keyword

MySQL supports executing SQL statements from other MySQL files. [Documentation](https://dev.mysql.com/doc/refman/8.0/en/mysql-batch-commands.html).
This can be done from a SQL query and uses either the `source` keyword or `\.` to specify the file to import:

```sql
mysql> source file_name
mysql> \. file_name
```

Dolt does not currently support this syntax. The syntax is also not mentioned on any Dolt help pages, so it's not immediately obvious whether dolt supports this approach or not.