Add Telemetry for Extension Finder SPIs

[mhlidd]

What Does This Do

This PR sends metrics for all OTel SPIs that are detected on the existing ExtensionFinder class. This effectively tracks any OTel SPI that is registered at any of the JAR files on the path listed by otel.javaagent.extensions or dd.trace.extensions.path.

Motivation

Additional Notes

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Jira ticket: [PROJ-IDENT]

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[amarziali]

can we exit here do avoid looping on entries if we already found?

[mcculls]

If the goal here is to report all service files under the OTel namespace then the best we could do is exit on the first entry that doesn't start with the services prefix. That's assuming that the service entries appear in a group, which they usually do. If assume that the service entries are ordered then we could exit on the next entry that doesn't start with the OTel namespace.

However I'd like to know about what we intend to gain from this telemetry since this will incur a non-trivial startup cost, albeit only when extensions are added to the tracer (which is uncommon.)

i.e. if the goal is to survey what SPIs are being added as extensions, even though we don't currently support them then I guess this is the only way to discover that (although it would be a good idea to short-circuit the searching when we get to jar entries that we know should appear after service entries - you can look at some example OTel extension jars to see if there's a pattern.)