improve local debugging

[tomerd]

with #73 and #87 we introduced the ability to start a local simulator which enables local debugging.

our initial approach was code based, ie call the withLocalServer function and gate it with #if DEBUG but that was deemed low usability
the current environment variable based approach is easy to use, but means users cannot be configured in a meaningful way, which we may want to do for example to inject middleware that simulate api gateway

we should explore more alternatives before 1.0