appsec: rework actions system

[Hellzy]

What does this PR do?

The goal is to centralize the action system and get rid of duplication in httpsec/grpcesec, especially when it comes
to the action handler (which is not a thing anymore with this change).

This change introduces 2 new methods to the operation interface:

• EmitData(), which sends data of any type to the operation's listeners
• OnData(), which register data listeners that will handle data when receiving it

The main use case of this API is to pass actions around between the WAF and our instrumentation points.
Another use case is to emit errors, which is especially usefull for our SDK instrumentations (userID, http parsed body)
which usually get called while in the request handler and are hence error based.

Motivation

This is a step in our effort to cleanup the code base and make it less intricate. While this adds more code that it deletes,
it gets rid of annoying side effects and weird mechanisms that were introduced in operations in order to transport actions
and errors.
The action system still remains quite complex due to the SDK instrumentation points that remain, as well as the
duality between grpc/http, and other intricacies due to other frameworks (such as echo).

Describe how to test/QA your changes

Reviewer's Checklist

• Changed code has unit tests for its functionality.
• If this interacts with the agent in a new way, a system test has been added.

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-07-06 08:39:29

Comparing candidate commit 267b872 in PR branch francois.mazeau/appsec-refactor with baseline commit 7f9ab67 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 27 metrics, 0 unstable metrics.