[server] Script to move threads

Summary:
I used this script to complete ENG-1860.

Figured it would be good to preserve for posterity.

Test Plan: I ran the script in production. The second updateThread call actually failed for this reason, but I figured I'd leave it in there as an example call.

Reviewers: atul

Reviewed By: atul

Subscribers: tomek, abosh

Differential Revision: https://phab.comm.dev/D5221