docs(api_gateway): new event handler for API Gateway and ALB

[heitorlessa]

Issue #, if available:

Description of changes:

Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics
• Create Getting Started example
• Create sample infrastructure for Proxy Event
• Create Examples section for high level methods
• Cover correlation ID in the getting started example
• Cover CORS for prototyping and production
• Mention CORS on errors like 404
• Cover integration with Data classes
  • query strings
  • headers, Lambda context
• Cover use of Response()
• Cover binary responses
• Cover GZIP responses
• Cover Testing
• Cover FAQ on when we recommend Chalice and fully fledged web frameworks
• ALB specifics
  • [x] Create sample infrastructure
    • ALB has no support for CloudFormation for Lambda as target
  • Demonstrate how to use ProxyEvent

Minor implementation changes

cc @michaelbrewer

• Enum to match code style (PascalCase)
• Keep not found only in message return for security reasons
• Remove Tuple type of response to keep it simpler (Dict and Response only)
• Create Example section (docstrings) for routes app.get, app.post, app.delete, etc. to improve DX on IDEs.

Breaking change checklist

RFC issue #:

• Migration process documented
• Implement warnings (if it can live side by side)

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 #418 (bcdf622) into develop (59b3adf) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #418   +/-   ##
========================================
  Coverage    99.89%   99.89%           
========================================
  Files          101      101           
  Lines         3977     3989   +12     
  Branches       198      197    -1     
========================================
+ Hits          3973     3985   +12     
  Misses           1        1           
  Partials         3        3           

Impacted Files	Coverage Δ
aws_lambda_powertools/event_handler/api_gateway.py	100.00% <100.00%> (ø)

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[heitorlessa]

Merging it now @michaelbrewer but I'll wait for your other PR to fix cors=None piece and I'll release it tomorrow morning.

[michaelbrewer]

LGTM. I will look at adding support for cors=None as the default at the route level.