Local execution for Lambdas

[72636c]

The lambda-sqs-worker template does not come with a skuba start script. This is because we haven't decided on a local execution experience for Lambdas. A few options in my current order of preference:

1. Serve the handler over HTTP so you can POST the input events. I consider this slightly better than option 2 because it's less boilerplate and lets you test container reuse scenarios.

2. Just require the entry point. This will likely mean that users will need to provide their own local wrapper around the Lambda handler, e.g.

   // localHandler.ts
   
   import { handler } from './app'
   
   handler({ event: 'my test event', context: 'my test context' })

3. A local Lambda runtime, e.g. proxying serverless invoke local. I'm not super keen on replicating the runtime locally or tying skuba to Serverless but could be convinced otherwise.