docs: Add docs for Neon PostgreSQL variant

[danthelion]

Description:

(Describe the high level scope of new or changed features)

Workflow steps:

(How does one use this feature, and how has it changed)

Documentation links affected:

(list any documentation links that you created, or existing ones that you've identified as needing updates, along with a brief description)

Notes for reviewers:

(anything that might help someone review this PR)

---

This change is 

[williamhbaker]

I kind of skimmed parts of these since they look like a copy/paste of the standard postgres docs, but overall LGTM.