Add ability to disable reactor instrumentation

[lmolkova]

Is your feature request related to a problem? Please describe.

Reactor instrumentation doesn't always do a great job. Here're some of the known problems:

• makes exception stacktraces unreadable (TracingSubscriber is added on every reactor operator)
• adds perf overhead
• sometimes propagates context in situations it's not really desireable.

All these could be good reasons to disable reactor instrumentation.
When using vanilla OTel agent, I can disable it with OTEL_INSTRUMENTATION_REACTOR_ENABLED=false env var or system property,
but it has no effect on ApplicationInsights agent.

Describe the solution you would like
We need an appInsights specific option to disable reactor instrumentation or allow to disable it with OTel one.

[jeanbisutti]

From 3.4.19 version, the Reactor instrumentation is supposed to be disabled with -Dotel.instrumentation.reactor.enabled=false. #3472 has been created to be able to do this with an environment variable.

[jeanbisutti]

@lmolkova OTEL_INSTRUMENTATION_REACTOR_ENABLED=false environment variable should in fact already disable the Reactor instrumentation from the 3.4.19 version.

[microsoft-github-policy-service]

This issue has been automatically marked as stale because it has been marked as requiring author feedback but has not had any activity for 7 days. It will be closed if no further activity occurs within 7 days of this comment.