Lambda Event to support Lex V2 API

[aneelamr]

Is your feature request related to a problem? Please describe.
Aws-lambda-go supports default events for Lex. The lex v1 api events are supported here
https://github.com/aws/aws-lambda-go/blob/main/events/lex.go

However, the event format is not backwards-compatible with Lex V2 API and a change of payload format can be found here
https://docs.aws.amazon.com/lex/latest/dg/message-lambda.html

Describe the solution you'd like
I would like events from Lex to support both V1 and V2 apis, even if these are seperate structs. This would be a much better customer experience

Describe alternatives you've considered
Alternative I considered is to Create 1 event that supports both Lex APIs, but this can be confusing to the customer.

Additional context
Migration Guide- https://docs.aws.amazon.com/lex/latest/dg/message-lambda.html