internal/telemetry: collect telemetry info for gorilla/mux integration

[lievan]

What does this PR do?

This PR implements collecting integration info for instrumentation telemetry. Currently it only tracks the gorilla/mux contrib package.

Unit testing for integration collection is done in contrib/internal/telemetrytest.

We also add a POC of a test (TestTelemetryEnabled) that verifies the expected contrib packages are importing telemetry.

Motivation

Collecting telemetry info for integrations will unlock a lot of useful data. In order to collect this data, we will have to add a call to telemetry.LoadIntegration inside an init function in every contrib package. This PR shows an example of how that might be done and tested in contrib/gorilla/mux. We can use this example to evaluate whether or not it is worth it to do this and maintain for every contrib package.

Describe how to test/QA your changes

There is currently a unit test in contrib/gorilla/mux, and we probably want to manual test with a sample app or with system tests as well. There is currently not a system test for integration collection.

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

Comparing candidate commit 3fe7096 in PR branch evan.li/integration-telemetry with baseline commit ccb4c6a in branch main.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 17 metrics, 0 unstable metrics.

scenario:BenchmarkConcurrentTracing-24

• 🟩 execution_time [-0.198ms; -0.181ms] or [-14.404%; -13.152%]

[katiehockman]

Yeah this is reasonable, and probably as minimally invasive as we're going to get. Thanks!! Just a few small comments.