Add options to allow port and listening interface to be changed

[adam-nielsen]

Small change to allow the port number to be changed in serverless.yml. Structure was borrowed from serverless-offline-s3-local.

[marconi1992]

Thanks for the PRs, everything is good just a concern with the serverless-offline configuration

[marconi1992]

We'll have port conflicts if we use serverless-offline + serverless-offline-lambda plugins at the same time because the server that emulates API gateway is a different one than for emulating Lambda invocations.

custom:
  serverless-offline:
    port: 4000

Using the configuration above the lambda server will try to use the same port than API Gateway.

[adam-nielsen]

I thought the same thing, but this is the way the offline S3 plugin works as well. I think it's actually a feature more than a bug, in that if you change the Serverless port only, things will fail because you then need to specify all the ports. I can't think of any other reason why they'd have done it that way, unless there are other Serverless config options that plugins may need to inherit?

[marconi1992]

Gotcha!! I didn't notice that on the S3 plugin before. Regarding the config options, nothing comes to mind so far, but I'll try to figure out what is missng and come back with something in this thread. thanks!!