Decouple otlp/otlpmetric/otlpmetricgrpc 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 package.

This is the first PR in accomplishing #4403.

Why not start with otlpmetric/internal like #4397?

The otlptrace packages are stable releases. That means otlptrace/internal cannot be removed in a backwards compatible manner.

The otlpmetric packages, however, are not stable releases. Therefore, the ultimate goal is to remove otlpmetric/internal and I don't want to waste any development effort templatizing it.

[codecov]

Codecov Report

Merging #4404 (1d276a9) into main (2e6ca0a) will decrease coverage by 0.5%.
The diff coverage is 76.6%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4404     +/-   ##
=======================================
- Coverage   83.5%   83.0%   -0.5%     
=======================================
  Files        206     217     +11     
  Lines      15982   17166   +1184     
=======================================
+ Hits       13359   14264    +905     
- Misses      2344    2611    +267     
- Partials     279     291     +12     

Files Changed	Coverage Δ
exporters/otlp/otlpmetric/otlpmetricgrpc/client.go	90.6% <ø> (ø)
exporters/otlp/otlpmetric/otlpmetricgrpc/config.go	41.8% <ø> (ø)
...porters/otlp/otlpmetric/otlpmetricgrpc/exporter.go	83.0% <ø> (ø)
...pmetric/otlpmetricgrpc/internal/otest/collector.go	23.2% <23.2%> (ø)
...lp/otlpmetric/otlpmetricgrpc/internal/oconf/tls.go	35.7% <35.7%> (ø)
...pmetric/otlpmetricgrpc/internal/oconf/envconfig.go	69.9% <69.9%> (ø)
...tlpmetric/otlpmetricgrpc/internal/oconf/options.go	84.0% <84.0%> (ø)
...ric/otlpmetricgrpc/internal/envconfig/envconfig.go	86.4% <86.4%> (ø)
...otlpmetric/otlpmetricgrpc/internal/otest/client.go	97.1% <97.1%> (ø)
.../otlpmetric/otlpmetricgrpc/internal/retry/retry.go	98.3% <98.3%> (ø)
... and 4 more

... and 1 file with indirect coverage changes