Exclude otel micrometer instruments from reading values

[laurit]

Hopefully resolves #15486
When using composite registry micrometer creates instruments for all registries and stores them in a map. Values are recorded to all instruments. When reading a value it reads from the first element of the map. This PR adds wrapping for the iterator that is used to find the first element of the map that skips over instruments from our registry. Note that this works only for the javaagent instrumentation.

[zeitlinger]

Great - I think this is a longstanding issue.

Can this issue also occur with library instrumentation, e.g. spring starter?

[laurit]

Great - I think this is a longstanding issue.

Can this issue also occur with library instrumentation, e.g. spring starter?

I believe it can. We are already doing something in https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/instrumentation/spring/spring-boot-actuator-autoconfigure-2.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/spring/actuator/v2_0/OpenTelemetryMeterRegistryAutoConfiguration.java I think we needed to make sure our registry is returned last so actuator could look into other registries first. We could also wrap all the instruments and have the methods that return value look up the instrument from the original registry and get the value from there.
Alternative would be to implement value in our instruments, but the problem with that is that there are multiple ways to compute these values and what we implement might not be the same as what the original registry uses.

[zeitlinger]

I think we needed to make sure our registry is returned last

Right - thanks for reminding me.
I think that's a good enough solution.