merge develop into production

• Specify ssh-keys as list of strings, rather than having a single string. (!254 (merged))
• Grafana: Payments dashboard log fix & fine tune (!260 (merged))
• Update nixpkgs. (!259 (merged), !252 (merged), !249 (merged), !247 (merged), !238 (merged), !231 (merged))
• Add a derivation that builds all three grids. (!253 (merged))
• Loki/Promtail: Towards centralized logging (!251 (merged))
• Auto-optimize nix stores on dev and staging VMs (!255 (merged))
• Use the qualified .monitoringvpn domains for collecting metrics. (!236 (merged))
• Update whetstone hostname to private.storage. (!250 (merged))
• Reorder issuer domains (!211 (merged))
• Add Tom's comments to the docs (!248 (merged))
• Speed up evaluation of grids by evaluating custom packages once. (!246 (merged))
• Grafana: Allow access to /metrics only to monitoring network and localhost (!242 (merged))
• Change yet another IP from 67 to 56 subnet (!243 (merged))
• Bump to PaymentServer 2022-01-17 (!244 (merged))
• Fix Grafana start on local dev after upgrade to NixOS 21.11 (!241 (merged))
• Minor factoring improvements to the tests (!239 (merged))
• Fix up local dev VM grid IPs to be in line with MR (!232 (merged))
• Update nixos to 21.11 (!222 (merged))
• Collect some monitoring host details automatically. (!234 (merged))
• update to the new host key (!235 (merged))
• Fix megacli2prom out-of-range error (!229 (merged))
• bump to the ZKAPAuthorizer branch that pulls in and is compat w/ the new Tahoe-LAFS (!230 (merged))
• Merge most of the code from the customize-*.nix nodes into the base modules. (!233 (merged))
• move all of the hosts from 192.168.67.x to 192.168.56.x (!232 (merged))