[wip] remove getModuleGroup

[SylvainJuge]

Work in progress draft to remove getModuleGroup.

Fixes #17720

Summary

• introduce a common InstrumentationModuleClassLoader instance for each instrumented classloader
• make this common classloader include all the agent classes in a list of known packages (hard-coded as a PoC)
• once we have validated this approach is what we aim to have, we can improve the packaging of the solution:
  • idea 1: use package-info.java + annotation to indicate using common classloader
    • this has the advantage to work transparently even with current class shading.
    • we could generate automatically package-info.java for all packages in libraries, hence making them loaded in the common CL. keeping this manual could also be fine as not all libraries are shared.
    • refactor current instrumentation to only rely on libraries for cross-instrumentation dependencies.
  • idea 2: use heuristic on the package name, for example with *.common.* but that sounds brittle and sensitive to minor inconsistencies in package names.

Step 1: verify we can rely on hard-coded package name.

• opentelemetry-api-bridge
• netty
• hibernate
• servlet
• pekko-server
• akka-http
• aws-sdk
• aws-sdk-v2
• couchbase
• elasticsearch

Step 2: implement a long-term solution

• Explicit class-loading target for instrumentation classes #18824

[JonasKunz]

Overall approach makes sense to me!
This approach allows to put the shared classes in a library, which can be shared across the modules to make the dependencies explicit.

One suggestion I would have is to maybe not use *.common, but something more obscure like otel_common. Thanks to indy, Instrumentation modules can use libraries/dependencies without polluting the instrumented classpath. The *.common package name pattern could be coincidentally used in those libraries, while for something like otel_common this won't happen.

[linux-foundation-easycla]

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