[FEATURE]: Add support for MERGE

### Describe what you want

The SQL standard supports [MERGE](https://modern-sql.com/caniuse/merge), and Postgres 15+ supports it under the hood.

Syntax:

```
MERGE
INTO [[AS] ]
USING [[AS] ]
ON

```

While one can raw-dog it, I think it would be really nice to see it in Drizzle. Something like this:

```ts
await db.mergeInto(tableName)
.usingValues(...upsertRecords) // of inferred insert type
.updateOnMatched(
($new) => ({
column: $new.value
})
)
.insertOnNotMatched(
($new) => ({
column: $new.value
other_column: $new.other_value
})
)
.returning()
```

Rough idea of course, but you get the point. A clean API to use the MERGE statement that will hopefully, one day, be available in all dialects.

Even though Drizzle aims to have a simple builder API, is this something that can be considered?