[FFS-4372] introduce simple rails app poc

[iannorriswork]

Plan:

• merge this code in as is, allowing either version to be deployed (Go or Rails version)
• deploy and test in dev to confirm that this works as expected
• run a followup PR that puts the rails code as priority and removes the Go code
• run a followup PR to finish up any shoryuken required changes and infra
• followup PR to add static analysis

questions:

• is it convenient to leave this in a Rails directory rather than have the Rails app be top level?

[iannorriswork]

we'll probably favor heavy environment variables over encrypted rails credentials, given the open source nature of things.

[jeffgreenland-cms]

Overall looks thorough from my review.

[iannorriswork]

Going to merge as in, but feel free to comment for necessary followup or questions.