Prevent `/context/system_info.json` from erroring before guided setup is complete

[grantfitzsimmons]

At the moment, databases that have not yet completed the Guided Setup process will error when attempting to reach the /context/system_info.json endpoint until setup is complete. The issue is that we depend on this endpoint for uptime monitoring, leaving us unable to accurately monitor the status of hosted instances until the process has finished.

Example: https://sp7demofish.specifycloud.org/context/system_info.json