Include SchemaURL in OTLP text

[tigrannajaryan]

This enables printing SchemaURL in logging exporter.

[codecov]

Codecov Report

Merging #4500 (e31a942) into main (aee2d67) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #4500   +/-   ##
=======================================
  Coverage   90.77%   90.78%           
=======================================
  Files         179      179           
  Lines       10412    10418    +6     
=======================================
+ Hits         9452     9458    +6     
  Misses        743      743           
  Partials      217      217           

Impacted Files	Coverage Δ
internal/otlptext/logs.go	100.00% <100.00%> (ø)
internal/otlptext/metrics.go	100.00% <100.00%> (ø)
internal/otlptext/traces.go	100.00% <100.00%> (ø)

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