Should own types for typescript support

[croconut]

For typescript lambdas that use this library and don't use aws-lambda, we end up having this extra, unused dependency. I resolve by marking it external for my bundler and not including it, but it would make sense and is more user-friendly to inline these types to the index.d.ts file.

my current workaround:

// in package.json
"build": "esbuild index.ts --bundle --external:aws-lambda --tree-shaking=true --format=cjs --platform=node --target=node16 --outfile=./build/index.cjs"