[PG, Neon] Add neon_identity integration

[pffigueiredo]

Description

This PR aims to add Neon Identity related databased objects to the drizzle-orm sdk, so that Neon users that want to use Neon Identity with Drizzle, can simply import the pre-defined schemas and don't need to define them by hand everytime.

FEATURES

• define neon_identity schema
• define and export users_sync table

Test Plan

Added a small test that asserts the schema, table name and columns included.
Also installed the local drizlzle-orm version and used to usersSync export to make sure everything worked fine.

Subscribers

cc @davidgomes

Issue

Relates to #3959

[davidgomes]

Looks good to me 😎

[pffigueiredo]

Also, I'm wondering if it makes sense to just export the users_sync type from here, or if we should let the consumers derive it 🤔