[APPSEC]: blocking for alb multi value headers events

[florentinl]

What does this PR do?

This PR fixes blocking for Appsec in the context of ALB events for lambdas in target groups with multi-value headers enabled:

• Add EventSubTypes for regular ALB and ALB multi-value headers to propagate the information
• Send a blocking response with multiValueHeaders instead of headers when required.
• When multi-value headers is checked
• [typo] renamed the sample events file

Motivation

While adding the ALB event types to the system-tests in : DataDog/system-tests#5181. I noticed that blocking responses did not work as expected in the multi-value headers case.

Testing Guidelines

• updated the unit tests
• ran the system-tests manually: pending lambda: add three new lambda events with python weblogs system-tests#5181 and [APPSEC]: fix Lambda not appearing on the Appsec API Security Endpoint Catalog #654

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)