Opentelemetry-specification: Add w3c TraceContext propagation integration tests

[srjames90]

What are you trying to achieve?
W3c has an external validator to verify that the TraceContext spec is adhered to https://github.com/w3c/trace-context/tree/master/test. Opentelemtry-python has already integrated these tests into their own repo (https://github.com/open-telemetry/opentelemetry-python/issues/202), and I think it'd be good to do something like this in all of the languages.

Additional context.
These are the relevant files in the opentelemetry-python repo:
https://github.com/open-telemetry/opentelemetry-python/blob/master/tests/w3c_tracecontext_validation_server.py
https://github.com/open-telemetry/opentelemetry-python/blob/master/scripts/tracecontext-integration-test.sh

I've already written similar validation servers to the python server but in Go, Java, and JS. They work with a modified version of the shell script above, just need to figure out how to integrate them into the different repos.

[tigrannajaryan]

This does not seem to be a specification issue. It is about adding integration tests to SDKs.

There is an open PR which attempts to add specification for tests: https://github.com/open-telemetry/opentelemetry-specification/pull/630

If this issue is indeed about coming up with a common specification about how the tests should be implemented (and not an issue to actually _implement_ the tests) then I think the description needs to be clarified.

Either way I do not think this is a must have to the GA (although highly desirable to have good test coverage). I suggest to remove release:required-for-ga label.

[andrewhsu]

From the issue triage mtg today, i'm changing the label to release:after-ga since it looks like from the comments this can be punted.