Support custom `CREATE DATABASE` statements

### Feature description

I'm developing an application which is highly sweden-centric. For this reason, I use the following setup:

```sql
CREATE DATABASE
dansdata
WITH
ENCODING 'UTF8'
LOCALE_PROVIDER icu
ICU_LOCALE "sv-SE"
TEMPLATE template0;
```

However, these settings are not respected when the database is recreated by `graphile-migrate`.

### Motivating example

I think it is important that migrations etc. are tested as close to production settings as possible.

### Supporting development

I [tick all that apply]:

- [ ] am interested in building this feature myself
- [ ] am interested in collaborating on building this feature
- [x] am willing to help testing this feature before it's released
- [ ] am willing to write a test-driven test suite for this feature (before it exists)
- [ ] am a [Graphile sponsor](https://www.graphile.org/sponsor/) ❤️
- [ ] have an active [support or consultancy contract](https://www.graphile.org/support/) with Graphile