feat: show stack traces when capturing errors in the handler

[Angelmmiguel]

Display JS stack traces when there's an error:

Before

There was an error running the handler:
TypeError: not a function

After

There was an error running the handler:
TypeError: not a function
    at errorHandler (handler.mjs:3748)
    at handleError (handler.mjs:3914)
    at dispatch (handler.mjs:3938)
    at <anonymous> (handler.mjs:3768)
    at <anonymous> (runtime.mjs)
    at requestToHandler (handler.mjs:2962)

It closes #246

[ereslibre]

Thanks!