A port for debugging and stepping into the code

When running the service locally it would be helpful to step into the code. This is possible when using SAM but not when we use container images and run the function using RIE.

Can you add a debug port mapping to be used? It can be enabled and disabled via the environment variable.

For example, when running usual java apps we can add `-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=*:5005` to the run command and then listen to 5005 to be able to step into the code.

I have previously created a [ticket](https://github.com/aws/aws-lambda-runtime-interface-emulator/issues/33) in the [aws-lambda-runtime-interface-emulator](https://github.com/aws/aws-lambda-runtime-interface-emulator) project. It was suggested that I reach out here instead.