add Akka Scheduler context propagation

[pjfanning]

Akka version of #12359 (#11755)

[pjfanning]

This isn't quite ready. I'll look into the issues tonight.

[pjfanning]

Build passing now.

[heyams]

this is just for my own curiosity: why getting the current context from Java8BytecodeBride?
why not 'Context.current()' directly?

[pjfanning]

This is what most of the code does so I did it too. Are you a regular contributor to this lib and if so, can you explain why I should change?

[pjfanning]

opentelemetry-java-instrumentation/docs/contributing/javaagent-structure.md

Line 43 in b184587

is instrumented with the javaagent; for example, the `Java8BytecodeBridge` that should be used

says to use Java8BytecodeBridge.currentContext() inside Advice classes.

I assume this includes here but I am a first time contributor so I will change this if any of the regular contributors say so.

[trask]

it's needed when the Advice is inlined into bytecode that targets a version of Java prior to Java 8

interestingly, I think it will no longer be needed after #11457 (since we will no longer be inlining our advice code)

the javadoc explains a bit more:

opentelemetry-java-instrumentation/javaagent-extension-api/src/main/java/io/opentelemetry/javaagent/bootstrap/Java8BytecodeBridge.java

Lines 13 to 17 in b184587

	* A helper for accessing methods that rely on new Java 8 bytecode features such as calling a static
	* interface methods. In instrumentation, we may need to call these methods in code that is inlined
	* into an instrumented class, however many times the instrumented class has been compiled to a
	* previous version of bytecode and so we cannot inline calls to static interface methods, as those
	* were not supported prior to Java 8 and will lead to a class verification error.

[heyams]

This is what most of the code does so I did it too. Are you a regular contributor to this lib and if so, can you explain why I should change?

i was not asking for a change.. just curious to know the reason behind. @trask explained it.

[pjfanning]

@trask The existing opentelemetry-java-instrumentation code for Akka and Pekko uses Java8BytecodeBridge. Is it ok if I stick this 'style' and that all the code can be changed to stop using Java8BytecodeBridge in a future commit?

[trask]

oh, definitely, it's totally fine to use Java8BytecodeBridge