Inconsistency on non_heap vs. nonheap value for memory metrics

[AlexanderWert]

Description

Describe the bug
In the semantic conventions for JVM runtime metrics (on the process.runtime.jvm.memory.* metrics) the attribute values for the type attribute are defined as heap and nonheap.

Here (in the Java instrumentation) the values are heap and non_heap (with underscore!) which is not what the semantic conventions define:

opentelemetry-java-instrumentation/instrumentation/runtime-metrics/library/src/main/java/io/opentelemetry/instrumentation/runtimemetrics/MemoryPools.java

Line 50 in 335e36d

private static final String NON_HEAP = "non_heap";

Steps to reproduce
Run the Java agent and observe the JVM memory metrics.

What did you expect to see?
The attribute values for type to be aligned with the semantic conventions.

What did you see instead?
non_heap instead of nonheap

What version are you using?
1.23.0

Environment
not relevant

Solution alternatives

1. Either fix it in the Java instrumentation / agent to comply with the semantic conventions
2. OR fix the semantic conventions to comply with the Java implementation.

Since this aspect of the semantic conventions only affects Java, Option 2 seems to be the simpler and less intrusive approach.

[laurit]

@jack-berg should we change semantic conventions or the code?

[trask]

+1 on using non_heap (I think that's most consistent)

i'll send a spec PR to float the proposal

[jack-berg]

Agreed on non_heap.

[trask]

done, thx for noticing this @AlexanderWert!