Upgrade Node JS from 16 to 18

[abdullahwaheed]

Abstract
Node 16's support will end on September 11, 2023. So we have to upgrade node JS to v18 before that.

Extras
Project should use .nvmrc to have a consistent node version
We have to update Readme accordingly.

Upgrade Node JS from 16 to 18

[feanil]

This repo will be removed as a part of openedx/public-engineering#227 so there is no need to do this upgrade. I'll leave the ticket here until the archival is complete so we're aware of it but I'm gonna remove it from the maintenance board.