Improve Node.js Functions programming model 🚀

[ejizba]

Goals

1. Be idiomatic for Node.js developers. Users should be able to look at the code and immediately know what's going on
2. Let users define their own file structure (related to Allow discovery of functions in nested directories azure-functions-host#5373)
3. Let users define function metadata in js/ts files instead of json
4. Take advantage of types as much as possible, including for JavaScript users (i.e. VS Code can provide Intellisense for JavaScript based on the TypeScript types as long as it can find them)
5. Model after an existing popular/modern framework (Fastify, Express, Firebase, Remix, etc.), but ideally be flexible enough to allow for other frameworks to be used

Plan of action

Moved to here: https://github.com/Azure/azure-functions-nodejs-worker/wiki/Roadmap#new-programming-model

Prototypes

See this repo for the example prototype: https://github.com/ejizba/func-nodejs-prototype