[instrumentation] - Add integration tests

[maorleger]

Packages impacted by this PR

@azure/opentelemetry-instrumentation-azure-sdk

Issues associated with this PR

Resolves #18738

Describe the problem that is addressed by this PR

This PR solves the following:

1. I would like to have an end-to-end test that uses our pipeline and ensures
   tracing works as expected. The idea here is to ensure we do not regress in the
   future when making core changes. I added a node-only integration test that uses
   core-rest-pipeline and a fake client.
2. We currently maintain a TestTracer, TestTracerProvider, and TestSpan
   independently in multiple places. OpenTelemetry already provides testing utils
   in their base package. I replaced our Test* objects with an InMemorySpanExporter
   which allows us to grab all exported spans and inspect them.
3. In-passing, I realized that for a bit there could be a drift between client
   packages that use the new naming conventions and core packages that use the old
   naming conventions to pull az.namespace into a span. While it doesn't feel
   appropriate to add compatibility code in our core packages, this package will be
   in beta for quite some time so I think it's fine to add it here temporarily.

Are there test cases added in this PR? (If not, why?)

Lots and lots

Checklists

• Added impacted package name to the issue description.
• Does this PR need any fixes in the SDK Generator?** (If so, create an Issue in the Autorest/typescript repository and link it here.)
• Added a changelog (if necessary).

[joheredi]

Looks good, I like the new test and how you are verifying that the call chain is correctly traced. Just left a small comment about the outer function name that threw me off initially when reading the tests.

[xirzec]

A few minor remarks, but I love that we're able to use more publicly provided goodies from OTel here.