lambda: add the possibility for different kind of events in the proxy

[florentinl]

Motivation

When running python_lambda scenarios, we are currently only serializing events as one kind of lambda events "API Gateway rest events".

The goal of this PR is to enable each weblog to choose which type of events it wants to receive from the LambdaProxyContainer.

Each weblog must have a way to request which event format it wants to receive from the LambdaProxy, starting with only one addtional event type to validate the design. The goal would be to eventually support all 5 kinds of lambda events that map to an http request:

• API Gateway rest
• API Gateway http
• ALB single header
• ALB multi header
• Lambda function URL

Changes

To do so, I propose adding a mandatory label in the Lambda weblog images that contains the expected type of event: lambda-proxy.event-type. The scenario then configures the proxy to send the correct type of event.

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

🚀 Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• If PR title starts with [<language>], double-check that only <language> is impacted by the change
• No system-tests internal is modified. Otherwise, I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added (or removed)?
  • Get a review from R&P team

[cbeauchesne]

Just a small variable rename, and it should be ok!