[Feature Request] Allow user to specify port

[timrs2998]

I'd like a -p or --port flag in the CLI to specify the port. I like that get-port has a preferred port option, although port 8080 is a pretty popular port so being able to change the default yarn dev port would be useful for local development and testing.

[jlengstorf]

I'm onboard with this. We'd effectively just need to add the flag, put it into the env, and check that with a fallback to 8080.

This could be a great first PR for someone — I'll label it and share it around. (Feel free to make the PR yourself as well.)

[timrs2998]

awesome thanks; I received that feedback internally and forwarded it as an issue upstream