[DOCS]: pgSchema part needs a section of configuriing `schemaFilter`

### Enhancement hasn't been filed before.

- [x] I have verified this enhancement I'm about to request hasn't been suggested before.

### Describe the enhancement you want to request

https://orm.drizzle.team/docs/sql-schema-declaration#schemas

After declaring a pgSchema table refering to this chapter, `pnpm exec drizzle-kit push` outputs: "[i] No changes detected".

I finally found the necessary config `schemaFilter` from `Ask AI`.

A paragraph on `schemaFilter` might be very helpful here.