prometheus: Add otel_scope_schema_url and otel_scope_[attribute] labels

[pellared]

Towards open-telemetry/opentelemetry-specification#4223 and #5846

• Add instrumentation scope schema URL as otel_scope_schema_url label to otel_scope_info metric
• Add instrumentation scope schema URL as otel_scope_schema_url label to "real" OTel metrics
• Add instrumentation scope attributes as otel_scope_[attribute] labels to "real" OTel metrics

Side notes:

• The exporter does not seem to work correctly if the end user adds e.g. an otel_scope_name attribute. I think the exporter should ignore all attributes with names that have prefix otel_scope_. This scenario is also not covered by the spec.
• I remember that David was also proposing to have the new functionality behind some env var feature toggle

[pellared]

@dashpole PTAL

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.6%. Comparing base (ff07838) to head (417330c).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5947   +/-   ##
=====================================
  Coverage   84.6%   84.6%           
=====================================
  Files        272     272           
  Lines      22864   22872    +8     
=====================================
+ Hits       19348   19356    +8     
  Misses      3172    3172           
  Partials     344     344           

see 1 file with indirect coverage changes

[pellared]

I was thinking about also adding otel_scope_ prefix for the otel_scope_info metric, but I feel that this would be a breaking change.

[dashpole]

Makes sense. There isn't really any purpose to the otel_scope_info metric anymore, since it duplicates labels already available on metrics.

[pellared]

What about backwards compatibility for OTel Collector Prometheus receiver? Jot needed as it is not stable?

[dashpole]

We can use an env var to gate the feature and allow migrating from otel_scope_info to otel_scope_. We probably shouldn't produce both at once.