Add compression support for otlp tonic

[BrynCooke]

Part of #774

Design discussion issue (if applicable) #

It looks like there needs to be a larger refactor to allow compression to be pushed up to ExportConfig and to have with_env set the variables to something that allows late binding. It'd be better to do this separately though as it affects all the settings in ExportConfig.

Changes

Adds the ability to use compression when using grpc-tonic.

Added support for the following env variables:

• OTEL_EXPORTER_OTLP_LOGS_COMPRESSION
• OTEL_EXPORTER_OTLP_TRACES_COMPRESSION
• OTEL_EXPORTER_OTLP_METRICS_COMPRESSION
• OTEL_EXPORTER_OTLP_COMPRESSION

This doesn't use with_env yet as it is impossible currently to detect at this point if compression is enabled for logs|metrics|traces.

Longer term we can add a new enum for use in ExportConfig like:

enum ConfigSetting<T> {
  Env,
  Some(T),
  None
}

Which would allow with_env to mark a field as being resolved by env variable. Thus allowing OTEL_EXPORTER_OTLP_LOGS_COMPRESSION to be used for logs, OTEL_EXPORTER_OTLP_TRACES_COMPRESSION for traces etc...

I'm happy to try to do this as a follow-up.

Follow up:
I just noticed that from_env was removed from the jaeger exporter, so maybe if we are going in the same direction with the otlp exporter then there's not need for the above.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Patch coverage: 67.5% and project coverage change: +0.2 🎉

Comparison is base (b28e41a) 49.4% compared to head (0dca7b4) 49.7%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1165     +/-   ##
=======================================
+ Coverage   49.4%   49.7%   +0.2%     
=======================================
  Files        164     165      +1     
  Lines      20445   20587    +142     
=======================================
+ Hits       10120   10248    +128     
- Misses     10325   10339     +14     

Impacted Files	Coverage Δ
opentelemetry-otlp/src/exporter/grpcio.rs	61.9% <ø> (+1.9%)	⬆️
opentelemetry-otlp/src/lib.rs	27.7% <ø> (ø)
opentelemetry-otlp/src/logs.rs	0.0% <0.0%> (ø)
opentelemetry-otlp/src/metric.rs	0.0% <0.0%> (ø)
opentelemetry-otlp/src/exporter/tonic.rs	75.0% <83.3%> (+3.3%)	⬆️
opentelemetry-otlp/src/span.rs	35.4% <83.3%> (+0.7%)	⬆️
opentelemetry-otlp/src/exporter/mod.rs	88.0% <95.2%> (+0.8%)	⬆️

... and 3 files with indirect coverage changes

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[djc]

This seems reasonable to me, thanks!