feat(lambda-http): create separate trait for lambda events body

[eduardomourar]

Issue #, if available: #472

Description of changes:

This will allow the extensions to be used outside the context of a service that passes the Lambda events body. The base trait will accept a default body, and a separate trait will be created specifically for the Lambda events body.

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.

[calavera]

Now that #491 has been merged, I think you're unblocked to work on this.

[calavera]

@eduardomourar let me know if you're interested in getting this change in the next release.

[calavera]

I'm carrying this over in #503, thanks for your contribution!

[calavera]

@eduardomourar let me know if you're interested in making this work, I don't completely understand in which cases this code should raise PayloadError::UnsupportedFormat or return Ok(None).

[hugobast]

@calavera I'll check with Eduardo if he doesn't have time to resume this, I'm interested, but I need a little bit of knowledge sharing first.

[hugobast]

I'll give an update on this PR today; sorry for the long delay

[hugobast]

@calavera, we can close this, I've played with this PR a bit, and what it offers is nice (i.e. a more permissive trait bound) but not strictly needed for our purpose at Stedi.

Caveat if you'd like this contribution though, I can update the PR and try to answer your questions. LMK

[calavera]

Thanks for looking into it. I'm going to close it if nobody really needs it for now.