[keyserver] Script to create new community

Summary: Eventually we'll want to add this to the UI, but for now a script is better than nothing. This is necessary for ENG-2416, and also something I called out in the Table stakes features doc on Notion.

Test Plan: Ran the script locally and confirmed that new community appeared in the navigation drawer on native

Reviewers: atul, ginsu, tomek

Reviewed By: ginsu

Differential Revision: https://phab.comm.dev/D6234