Consider removing `#[serde(deny_unknown_fields)]` from request types

[ramosbugs]

#666 added #[serde(deny_unknown_fields)] to ApiGatewayProxyRequest and other request types:
https://github.com/awslabs/aws-lambda-rust-runtime/blob/d513b13b4c48122602c0690f55147607f3bcc0da/lambda-events/src/event/apigw/mod.rs#L16

Using this serde attribute causes deserialization to fail if any unexpected fields are included in the request payload. This has two negative consequences:

1. Due to Bug: sam local includes extraneous version attribute in ApiGatewayLambdaEvent (incompatible with aws-lambda-rust-runtime) aws-sam-cli#6442, Lambda functions written using this library cannot be tested with versions of sam local from the past 3 years. This is a bug in aws-sam-cli, not the aws_lambda_events crate, but it illustrates a downside to strict request parsing.
2. If the Amazon API Gateway team were to add a new feature that involved a new request field, all deployed Rust Lambda functions using the Lambda proxy integration might immediately break in production. In most APIs, adding a new field is not considered a breaking change. Unless there's a guarantee from that team never to add additional fields, this could be a ticking time bomb.

Unless there's a strong reason to reject request payloads with unknown fields that outweighs these downsides, I'd recommend removing deny_unknown_fields.

[calavera]

I don't really remember why I added those attributes, and I don't have a strong opinion about it. Feel free to open a PR.

[github-actions]

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