Add support for `limit null` clause

### What version of `drizzle-orm` are you using?

0.28.5

### What version of `drizzle-kit` are you using?

0.19.13

### Describe the Bug

Using postgres .limit(null) produces error:

Argument of type 'number | null' is not assignable to parameter of type 'number | Placeholder'.
Type 'null' is not assignable to type 'number | Placeholder'.ts(2345)

But SELECT * FROM x LIMIT null is valid syntax

### Expected behavior

It should not error in typescript

### Environment & setup

Svelte Drizzle ORM. Just making a normal query