Decouple otlp/otlpmetric/otlpmetricgrpc and otlp/otlpmetric/otlpmetrichttp from otlp/internal and otlp/otlpmetric/internal using gotmp

[MrAlias]

Currently the otlp exporters share internal packages across package boundaries. This is something we want to stop doing: #3846. This PR addresses the cross-module internal package use for the otel/exporters/otlp/otlpmetric/otlpmetricgrpc otel/exporters/otlp/otlpmetric/otlpmetrichttp packages.

Additionally, it deprecates the otlpmetric/internal packages.

This PR is quite large. The plan is to break it apart and use this as the "road map" of where those subsequent PRs are going.

[codecov]

Codecov Report

Merging #4403 (b6d3457) into main (d1f33f1) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #4403   +/-   ##
=====================================
  Coverage   83.4%   83.4%           
=====================================
  Files        229     229           
  Lines      18645   18645           
=====================================
  Hits       15551   15551           
  Misses      2775    2775           
  Partials     319     319           

Files Changed	Coverage Δ
exporters/otlp/otlpmetric/internal/exporter.go	67.2% <ø> (ø)
...xporters/otlp/otlpmetric/internal/oconf/options.go	79.8% <ø> (ø)
exporters/otlp/otlpmetric/internal/otest/client.go	97.1% <ø> (ø)
...orters/otlp/otlpmetric/internal/otest/collector.go	6.9% <ø> (ø)

... and 2 files with indirect coverage changes