Set Schema URL when exporting traces to OTLP

[tigrannajaryan]

We previously were recording the Schema URL but were not setting
the recorded value when exporting. This change now uses the recorded
value when exporting to OTLP.

[codecov]

Codecov Report

Merging #2242 (884c2d7) into main (ec26b55) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #2242   +/-   ##
=====================================
  Coverage   72.4%   72.5%           
=====================================
  Files        168     168           
  Lines      11766   11768    +2     
=====================================
+ Hits        8530    8532    +2     
  Misses      3001    3001           
  Partials     235     235           

Impacted Files	Coverage Δ
...ers/otlp/otlptrace/internal/tracetransform/span.go	96.7% <100.0%> (+<0.1%)	⬆️

[tigrannajaryan]

@Aneurysm9 @MrAlias This does not change anything in the API, but it changes OTLP exporter behavior. Do we need a CHANGELOG entry for this?

[Aneurysm9]

I think a changelog entry for this would be good as it can allow people to discover when a capability was added.

[jmacd]

Thanks; also note #2197 plumbs the instrumentation library schema through to the OTLP exporter for metrics, so that its schema URL can be set in the corresponding message.

[tigrannajaryan]

Changelog entry added.

[tigrannajaryan]

I think this is ready to be merged.