Have codegen search for example events by replacing "_" with "-" and vice-versa

[LegNeato]

The event codegen tool looks for example json in the go project and synthesizes tests in rust when found. Sadly, sometimes the go example events aren't consistent so we have had to add some manual overrides:

https://github.com/srijs/rust-aws-lambda/blob/master/aws_lambda_events_codegen/src/main.rs#L116

Looking at the overrides, most can be removed if the locating logic could swap out "_" for "-" and vice-versa when searching.