Add note about v1.0 and v2.0

[tyrw]

From a user who had to change the default code:

It is the payload format version and looks like your sample code is setup to use v1.0:

https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-lambda-authorizer.html

• Add a note about using v1.0 vs v2.0
• Add another index file for whichever version is not used as the default in the guide. E.g. index-v2.js