Merge staging into production

• Split public and private keys (!114 (merged) and !116 (merged))
• Add payment server monitoring (!117 (merged))
• Minor nix-shell improvements (!111 (merged))
• CI improvements for docs (!113 (merged))
• Swap re-configuration (!103 (merged))
• morph node name simplification (!110 (merged))
• Refactored morph grid definition (!109 (merged))
• GSuite SSO for Grafana (!120 (merged))
• Upgrade systems to NixOS 21.05 (!121 (merged))
• Continuous deployment system (!115 (merged))
• Disable Grafana statistics reporting (!119 (merged))
• Try to fix the continuous deployment configuration (!124 (merged))
• Attempt to fix GitLab continuous deployment configuration (!126 (merged))
• Attempt to fix GitLab continuous deployment configuration (!128 (merged))
• Propagate morph exit status out of update script (!132 (merged))
• Supply ssh host keys to deployment script (!130 (merged))
• Prevent <nixpkgs> path from growing until it breaks nix tools (!131 (merged))
• Fix permissions on the deploy key so continuous deployment can authenticate (!134 (merged))
• Fix usage of the deploy key environment variable (!136 (merged))
• Fix whitespace problems with the deploy key that prevent it from being used (!138 (merged))
• Set initial Grafana web admin password (!123 (merged))