[terraform] Ensure only one running ecs task for primary service

Summary:
By setting the deployment maximum percent and minimum to 100 and 0, we ensure that there is only one primary node at a given time

The defaults were originally 200 and 0 percent which is meant for rolling updates; however, in our case we likely don't want two primary nodes running at the same time

Depends on D12708

Test Plan: On a terraform redeploy, all tasks were stopped and a single pending task was initialized

Reviewers: varun, bartek

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12709