fix grpc set metadata multi-value

[wgy035]

Resolves #11237
removeAll key before put in grpc MetadataSetter

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: wgy035 (91ff56b, 9bb816f, 4e54e1e, 8c2042c, 035dad3)
• ✅ login: laurit / name: Lauri Tulmin (9ceb0fb)

[steverao]

@wgy035 Please sign the CLA.

[trask]

@wgy035 can you add a test for this? (check out #2727 for possible inspiration)

[wgy035]

Got it. And now I'm trying to add a test.

[steverao]

Suggested change

	public static final String FIELD = "X-grpc-field";
	private static final String FIELD = "X-grpc-field";

[wgy035]

done

[steverao]

Suggest to use static import here, for more style guidance you can refer to
https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/docs/contributing/style-guideline.md#static-imports

[wgy035]

helpful suggestions

[steverao]

I would define a more meaningful name here, if it's hard to do here, is the propagator a better choice than now?

[wgy035]

I've already change the name

[laurit]

@wgy035 I have crated a PR for your PR wgy035#1 that changes the test so that it uses a standard propagator and verifies that injecting the tracing context twice results in the last inject overwriting the first one.