[terraform] Ensure that the primary service is running before deploying secondary service

Summary:
In writing the migration script, I realized that we likely want the primary node to run before the secondary nodes run on the very first deployment as well.

This accomplishes ordering the secondary node deployments behind the first by checking for a 200 OK on https://wyilio.com/health.

Depends on D12729

Test Plan:
I terraform destroyed my self-host setup and ran through an initial deployment. This script looped before creating the secondary keyserver service.
I had to add the new load balancer endpoint to my squarespace dns rules and waited for the primary node to come online. Once online, the script
received a status 200 OK and continued in creating the secondary nodes.

Reviewers: varun, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12730