Rewrite app to use NestJS

[jrm86]

As a developer/maintainer, I need to rewrite this app using the NestJS framework, so that I can more easily maintain it over time

This is done when:

• Tests for existing behavior are written
• Service(s), Controller(s), and Module(s) are written which replace existing behavior
• All code is valid TypeScript with appropriate function and argument typing (create custom types/objects as needed)
• All tests pass