Add events pass-through feature in lambda-http crate

[bnusunny]

Issue #, if available:

Related to awslabs/aws-lambda-web-adapter#216 and awslabs/aws-lambda-web-adapter#317

Description of changes:

To support addtional event triggers in lambda web adapter, such as SQS or Bedrock Agents, we need to pass-through events from those triggers. This PR adds a pass_through feature to lambda-http crate. When enabled, the events payloads will be translated to a HTTP post request (event payloads in the request body).

This PR also improves the deserializer.rs. It uses RawValue to get the data from deserializer, not relaying on private serde functions.

By submitting this pull request

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I confirm that I've made a best effort attempt to update all relevant documentation.

[github-actions]

👋 It looks like your code has some linting issues.

Please run cargo clippy --fix and push the code again.

[calavera]

I really don't understand why people prefer these kind of hacks to separated functions that do one thing, but I'll disagree and commit.

[bnusunny]

Thanks!