Add HttpSender abstraction

[jack-berg]

Part of #5351.

This is the first of several phases. Adds HttpSender interface, with OkHttpHttpSender implementation. All of this still lives in opentelemetry-exporter-common so this is just a refactor with no functional change at this point.

[codecov]

Codecov Report

Patch coverage: 90.05% and project coverage change: +0.02 🎉

Comparison is base (9bc34d7) 91.31% compared to head (d9cdfbd) 91.34%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5505      +/-   ##
============================================
+ Coverage     91.31%   91.34%   +0.02%     
- Complexity     4892     4893       +1     
============================================
  Files           547      546       -1     
  Lines         14412    14432      +20     
  Branches       1354     1351       -3     
============================================
+ Hits          13161    13183      +22     
+ Misses          866      863       -3     
- Partials        385      386       +1     

Impacted Files	Coverage Δ
...rter/otlp/http/metrics/OtlpHttpMetricExporter.java	84.61% <ø> (ø)
...telemetry/exporter/internal/http/HttpExporter.java	78.18% <78.18%> (ø)
...ry/exporter/internal/http/HttpExporterBuilder.java	90.69% <90.69%> (ø)
...try/exporter/internal/okhttp/OkHttpHttpSender.java	98.43% <98.43%> (ø)
...elemetry/exporter/internal/auth/Authenticator.java	100.00% <100.00%> (ø)
...entelemetry/exporter/internal/retry/RetryUtil.java	100.00% <100.00%> (ø)
...rter/otlp/http/logs/OtlpHttpLogRecordExporter.java	77.77% <100.00%> (ø)
...lp/http/logs/OtlpHttpLogRecordExporterBuilder.java	90.00% <100.00%> (ø)
...lp/http/metrics/OtlpHttpMetricExporterBuilder.java	95.23% <100.00%> (ø)
...exporter/otlp/http/trace/OtlpHttpSpanExporter.java	77.77% <100.00%> (ø)
... and 1 more

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[jkwatson]

I've had to create this thing in multiple projects now. It's almost like the java ecosystem needs an http client equivalent of slf4j. 🤔

[jack-berg]

jdk http client theoretically could put the "which http client" question to rest. Needs performance to be very competitive though, and probably full support for http2 (i.e. trailing headers)..

[jkwatson]

And be based on an interface, not an abstract class. 😿

[jkwatson]

since this is still internal, it's probably fine to just have this sitting here for now, but I would imagine we might want to create a "HttpMetadata" interface or something to pass in here, which might need to include more headers/etc in the future.

[jkwatson]

Thanks!