Camel 23283 micrometer span scope

[beskow]

Description

Pull request to correct behavior reported in https://issues.apache.org/jira/browse/CAMEL-23283:

When using camel-observability or camel-micrometer-observability, traces and spans are correctly created and exported for routes triggered by other, tracing-aware framework components (e.g. http). If a route is triggered by a jms message, no trace or span is exported however.

This seems to be caused by missing scope management: MicrometerObservabilitySpanAdapter::activate() only calls span.start() but doesn't put the
span into the tracer's thread-local scope. This means tracer.currentSpan() returns null during route execution, hence the span is invisible to downstream instrumentation that relies on tracer.currentSpan() to find a parent span.

The first commit adds a test to highlight the problem.
The second commit corrects the root cause of the problem, but cause side effects for other tests (the async test cases) which leaks trace information between test execution.
The third commit prevents leaked trace information from being propagated.

Target

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Tracking

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Apache Camel coding standards and style

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• I have run mvn clean install -DskipTests locally from root folder and I have committed all auto-generated changes.

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