Centralize the retry package for the otlp exporters

[MrAlias]

Part of #2015

With #2425 merged, the otlptrace and otlpmetric retry packages and use of that package are the same. This remove the duplicate code. It creates a unified exporters/otlp/internal/retry module that both modules can depend on. It is created as a module and not a package of the go.opentelemetry.io/otel module in order to isolate the dependency on the backoff package it uses.

[codecov]

Codecov Report

Merging #2427 (58cf4de) into main (f4b63f1) will decrease coverage by 0.1%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            main   #2427     +/-   ##
=======================================
- Coverage   75.6%   75.4%   -0.2%     
=======================================
  Files        175     174      -1     
  Lines      12170   12113     -57     
=======================================
- Hits        9201    9141     -60     
- Misses      2720    2723      +3     
  Partials     249     249             

Impacted Files	Coverage Δ
exporters/otlp/internal/retry/retry.go	98.2% <ø> (ø)
...ers/otlp/otlpmetric/internal/otlpconfig/options.go	52.9% <ø> (ø)
exporters/otlp/otlpmetric/otlpmetricgrpc/client.go	97.7% <ø> (ø)
...xporters/otlp/otlpmetric/otlpmetricgrpc/options.go	78.2% <ø> (ø)
exporters/otlp/otlpmetric/otlpmetrichttp/client.go	78.7% <ø> (ø)
...xporters/otlp/otlpmetric/otlpmetrichttp/options.go	69.2% <ø> (ø)
...ters/otlp/otlptrace/internal/otlpconfig/options.go	52.9% <ø> (ø)
exporters/otlp/otlptrace/otlptracegrpc/client.go	97.7% <ø> (ø)
exporters/otlp/otlptrace/otlptracegrpc/options.go	78.2% <ø> (ø)
exporters/otlp/otlptrace/otlptracehttp/client.go	83.3% <ø> (ø)
... and 2 more