[keyserver] Launch NSE for build 199 and above

Summary:
Builds 199-202 (inclusive) had some known issues, but none with NSE. So I figure it's safe to launch NSE on them.

We could alternately "play it safe" by only launching NSE for the latest public release (203 and above) while keeping NSE for the existing staff releases (200 and 202), but I figure that check would be too messy and it's not really necessary. But open to it if people think it's a good idea.

Test Plan: We tested the use of NSE by initially limiting its release to internal builds

Reviewers: marcin, atul

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7164