[otlp-exporter] Update support wording in README to state protocol version instead of collector version

[pichlermarc]

Currently, the exporters state a minimum and maximum supported collector version, for instance:

This module provides exporter for node to be used with OTLP (grpc) compatible receivers. Compatible with opentelemetry-collector versions >=0.16 <=0.50.

This refers to the last (manually) tested version; newer versions may actually work fine as long as the protocol version is compatible. We should change the wording to state the supported emitted protocol version instead. In case of a stable protocol, we should state that the exporter also supports later versions of this protocol.

Additional information:

• currently, we're using proto definitions v0.18.0
• JSON is not marked as stable for the version we're currently using (v0.18.0). Therefore we should not guarantee that later versions are supported by the JSON exporters.

[dyladan]

Are you sure we can't guarantee later versions? The trace, metric, and log protocols are all stable.

[pichlermarc]

Are you sure we can't guarantee later versions? The trace, metric, and log protocols are all stable.

This is only for JSON, and as long as we don't update to v0.19.0. As soon as we bump our proto submodule to 0.19.0 we can also guarantee stability for JSON 🙂

[pichlermarc]

After reading through the comment on #3712, I now think just stating the protocol version we're emitting would be sufficient. I updated the original issue text to reflect this.

Probably 18. I was looking through the proto diffs and there are some changes that might affect compatibility. Not entirely sure as I'm not a proto expert but we should probably just make the guarantee we're sure about and leave the rest to the user to decide. We're emitting version 0.18 proto.

Originally posted by @dyladan in #3712 (comment)

[github-actions]

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