Make muzzle reference creation package(s) configurable

[pavolloffay]

The instrumentationMuzzle is created only for instrumenters in io.opentelemetry.instrumentation.

opentelemetry-java-instrumentation/javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/muzzle/ReferenceCreationPredicate.java

Line 15 in dadaac9

private static final String REFERENCE_CREATION_PACKAGE = "io.opentelemetry.instrumentation.";

In my custom java agent build I am adding instrumentations in a different package and these instrumentations should have also instrumentationMuzzle properly created.

The package prefixes could be configured via a system property which would be set at build time. I don't think we need an SPI for it.

[mateuszrzeszutek]

It needs to be available both in compile-time and runtime - ReferenceMatcher is also using this predicate.

Are these the same packages as in BootstrapPackagePrefixesHolder?

By the way, I'm thinking that maybe we need to have some sort of AgentInternalConfig class that groups all such properties together, and a single SPI for changing that config (similar to TracerCustomizer). This way a vendor distribution could configure all its needs in a single place.

[pavolloffay]

Are these the same packages as in BootstrapPackagePrefixesHolder?

no, the packages in BootstrapPackagePrefixesHolder are different (not instrumentation) - these are classes that provide common functionality for instrumentations.

[mateuszrzeszutek]

Another idea based on: #2524 (comment)

Right now if we want to include a 3rd party library instrumentation in the javaagent (e.g. couchbase 3.1 instrumentation) we're forced to add all classes used in the library instrumentation as additionalHelperClassNames().
That's because muzzle collects neither helper classes nor references (used symbols) from 3rd party packages/classes.

To fix that a new customization point should be introduced to the InstrumentationModule: a method that returns a Predicate<String> (or similar) that returns a predicate determining whether a passed class name refers to an instrumentation helper class. The default behavior would be the current one e.g. InstrumentationClassPredicate.

To sum it up, instead of using SPI (as proposed above) we should allow customizing this behavior per instrumentation module.