Allow implementations to use their own default for OTLP compression.

[carlosalberto]

As discussed in yesterday's Spec SIG call, allow SIGs to define their own default. Specially important as OTel JS will be going GA very soon, and we want to allow it to use gzip as their default (at least for the browser case) - also a motivating reason to include this change in this week's Specification release.

(Also removed the mention of SIGs supporting other compression methods, as they should be vetted first by the Collector, etc)

Alternative to #1895

cc @dyladan @bogdandrutu

[codeboten]

👍

[dyladan]

This looks good from JS perspective. Sorry for late review i had vacation

[tigrannajaryan]

As discussed in the SIG, I think the best that we do this:

• The OTLP protocol spec to require all OTLP receivers to support both "none" and "gzip" compression.
• The SDK spec to allow SDKs exporters to use "none" or "gzip" as the default compression method when OTEL_EXPORTER_OTLP_TRACES_COMPRESSION env variable is unspecified. The choice of the default is language-specific.

[carlosalberto]

@tigrannajaryan Updated it to match the feedback, please review again.

@dyladan FYI, now the new explicit none option exists (besides gzip).

[tigrannajaryan]

LGTM, except the "none" part.

[carlosalberto]

@tigrannajaryan @yurishkuro Used none for no compression now. Please confirm so we can go ahead and merge.