add otlp trace http exporter

[paivagustavo]

Follow up from #1922.

This implements a HTTP otlptrace.Client.

Next steps

This is part of the #1827 todo list:

• add gRPC otlp trace exporter
• add HTTP otlp trace exporter
• add gRPC otlp metrics exporter
• add HTTP otlp metrics exporter
• refactor out the duplicated code (transform, connection, otlpconfig)
• update examples and remove old otlp gRPC/HTTP exporter
• update docs

[codecov]

Codecov Report

Merging #1963 (adb0d3f) into main (a75ade4) will increase coverage by 0.2%.
The diff coverage is 90.9%.

@@           Coverage Diff           @@
##            main   #1963     +/-   ##
=======================================
+ Coverage   76.3%   76.5%   +0.2%     
=======================================
  Files        157     160      +3     
  Lines       8363    8495    +132     
=======================================
+ Hits        6385    6505    +120     
- Misses      1723    1732      +9     
- Partials     255     258      +3     

Impacted Files	Coverage Δ
...ters/otlp/otlptrace/internal/otlpconfig/options.go	75.6% <ø> (ø)
exporters/otlp/otlptrace/otlptracehttp/exporter.go	0.0% <0.0%> (ø)
exporters/otlp/otlptrace/otlptracehttp/client.go	93.2% <93.2%> (ø)
exporters/otlp/otlptrace/otlptracehttp/options.go	100.0% <100.0%> (ø)

[MadVikingGod]

Other than the Exported constants I think this is good to go.

[MrAlias]

Nothing blocking.

[hanyuancheung]

LGTM