Run AWS handler for Elastic Serverless Forwarder locally

**Describe the enhancement:**

Provide a way to run the lambda handler locally accepting different kind of trigger events.
Ideally we will be able to run the handler from an IDE with a debugger attached.

**Describe a specific use case for the enhancement or feature:**

Currently you need to deploy a new version of the lambda in SAR on a development account and test a payload through AWS console. Or wrap your own `__main__` entry-point that's not versioned if you want to run locally/with debugger.

This is far from ideal and providing this feature will improve developers experience.