Migrate to using go.opentelemetry.io/proto/otlp

[MrAlias]

Changed

• Migrate from using internally built and maintained version of the OTLP to the one hosted at go.opentelemetry.io/proto/otlp.
• Migrate from using github.com/gogo/protobuf to google.golang.org/protobuf to match go.opentelemetry.io/proto/otlp.

Resolves #1585
Resolves #1393
Resolves #1324

[codecov]

Codecov Report

Merging #1713 (bb86538) into main (5d559b4) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #1713   +/-   ##
=====================================
  Coverage   77.8%   77.8%           
=====================================
  Files        131     131           
  Lines       6986    6985    -1     
=====================================
+ Hits        5438    5439    +1     
+ Misses      1298    1296    -2     
  Partials     250     250           

Impacted Files	Coverage Δ
exporters/otlp/internal/otlptest/collector.go	88.8% <ø> (ø)
exporters/otlp/internal/otlptest/otlptest.go	74.5% <ø> (ø)
exporters/otlp/internal/transform/attribute.go	91.6% <ø> (ø)
...porters/otlp/internal/transform/instrumentation.go	100.0% <ø> (ø)
exporters/otlp/internal/transform/metric.go	80.6% <ø> (ø)
exporters/otlp/internal/transform/resource.go	100.0% <ø> (ø)
exporters/otlp/internal/transform/span.go	98.1% <ø> (ø)
exporters/otlp/otlpgrpc/driver.go	90.1% <ø> (ø)
exporters/otlp/otlphttp/driver.go	93.8% <100.0%> (-0.1%)	⬇️
exporters/otlp/otlpgrpc/connection.go	88.7% <0.0%> (+1.8%)	⬆️