Support CREATE EXTENSION in postgres

### Dialect

PostgreSQL

### Failing SQL

```sql
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";

CREATE EXTENSION hstore SCHEMA addons;
```


### Description

As described here: 
https://www.postgresql.org/docs/10/sql-createextension.html

note the difference between v10 and v14: 
https://www.postgresql.org/docs/14/sql-createextension.html