Feature: Expose Lambda Extension package

[MovieStoreGuy]

Context

In order to allow the lambda extension work to be included in other external projects, it isn't completely clean (but gives a minimal required code changes).

Changes

I wanted to get some feedback before I commit to finishing it, the checked parts are done, the unchecked are what I'd like to do if we are okay with the direction.

• [x] Adds new package pkg/lambda that exposes a small subset of functionality
• [x] Added tests
• [ ] Replaces invocation in cmd/lambda-extension

[MovieStoreGuy]

I'll add the replace in cmd/lambda-extension in a future PR