#887 otlp exporter exemplars

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@fstab
This PR adds support for exemplars in the OTLP Exporter
Addressed #877

The change seems fairly trivial, but I wonder if we need more test coverage?

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Is there a reason why we are using JUnit 4, not 5?

[fstab]

Thanks a lot, it's looking great.

One tiny thing: There's an empty file trace.proto which I think is not needed.

Regarding tests: I like your test, it's a good way to test this. I know that test coverage of the OTel exporter is currently not great. For the Prometheus formats the ExpositionFormatsTest is much more complete, but it was also a lot of work :).

Is there a reason why we are using JUnit 4, not 5?

No, it's just that nobody updated it. If you like to create a PR: I'd appreciate an update to JUnit 5 :)

[0x006EA1E5]

One tiny thing: There's an empty file trace.proto which I think is not needed.

Removed, sorry about that

[0x006EA1E5]

@fstab Are there any more actions you need me to do here? Is it suitable to me merged as is?

[fstab]

Looks great, thanks a lot!