Support http.Handler for RESPONSE_STREAM Lambda Function URLs

[bmoffatt]

Issue #, if available:

#500

Description of changes:

Introduces a new package github.com/aws/aws-lambda-go/lambdaurl implementing an http.Handler based programming model for Lambda Function URLs configuered with InvokeMode: RESPONSE_STREAM

Decided follow the approach we chose for the github.com/aws/aws-lambda-go/cfn package. That package exposes a Wrap function that handles the translation of CloudFormation's unique programming model into the request/response+error model supported by github.com/aws/aws-lambda-go/lambda.Start.

API Gateway (V1/V2), ALB Targets, and InvokeMode: BUFFERED, are explicitly not supported.

1. Today, it's not possible to tell within the function which InvokeMode the request came in with.
2. Supporting InvokeMode: BUFFERED has a diminishing benefit - there's no reason I know of to choose BUFFERED for new applications
3. Supporting API Gateway (V1/V2), ALB Targets, is more scope than I can chew off in this PR, and has a diminishing benefit given that both can be configured to proxy to a Lambda Function URL

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-commenter]

Codecov Report

Merging #503 (1650763) into main (81d63bd) will increase coverage by 1.05%.
The diff coverage is 90.19%.

@@            Coverage Diff             @@
##             main     #503      +/-   ##
==========================================
+ Coverage   71.38%   72.43%   +1.05%     
==========================================
  Files          22       24       +2     
  Lines        1307     1375      +68     
==========================================
+ Hits          933      996      +63     
- Misses        306      310       +4     
- Partials       68       69       +1     

Impacted Files	Coverage Δ
lambdaurl/http_handler.go	90.19% <90.19%> (ø)

... and 1 file with indirect coverage changes

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[bmoffatt]

#504

[bmoffatt]

Will get back to this in the follow-up for all returned writers. As for now allowing the panic to crash the process and log is the "most correct" thing do do, at least compared to swallowing it without any logging / reporting!