Feature request: export "main" entrypoint to allow using it directly instead of using the cli

[cctidal]

I'm interested in using the main entrypoint function directly instead of using the cli to start up the function, mostly on the development environment.

This has some advantages, among others:

• Can be started with node directly: node src/server.js
• Can use node watcher, no need for extra setup with nodemon&others: node --watch src/server.js
• Better typescript support with ts-node/tsx: tsx --watch src/server.ts

This server.js would use the exported main entry point:

import {main} from 'functions-framework'

import {handle} from './index.js'

main(handle)

I'd be willing to implement this feature