[hf] migrate to new server 2021 01 27

• migrate prod and backup to new servers
• add playbook for migrating prod to /docs dir
• take advantage of the occasion of migration to rotate keys and other credentials
• take advantage of bigger server to bump signald shards back up to 8 (from 5)
• fix bug in which letsencrypt was not persisting cert data (causing us to get rate-limited after 5 restarts b/c it was requesting new certs every time)
  • also fix underlying cause of bug in which we used an unpinned version of the LE container (and thus started using a container that was looking for certs in a different place without knowing it!)
  • migrate to new subdomains (as a workaround for getting rate-limited on old ones by LE bug)
• change ansible tooling to make it easier to iterate on deploying new IPs to prometheus for scraping (without requring an MR to do so)
• various other tidying up of our deploy scripts