Razzle: PORT_DEV

~📖 Documentation~ Feature request

I have a monorepo and I'm setting it up with multiple packages that each use razzle. I was confused as to why I couldn't get them all to run in dev mode at the same time (each package is using a different sequential PORT value).

After a bit of digging I realised that the secret sauce was the cause of my issues 😄 (implicitly choosing the next sequential port as the dev port).

After a little more digging I've found PORT_DEV in the code here but it's not documented.

EDIT: turns out although although the reference to PORT_DEV exists in the code it doesn't seem to be used anymore? I'd like to suggest making it work and adding it to the docs