add new env config options for OTLP exporter

[seankhliao]

spec: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md#configuration-options

Add the INSECURE CLIENT_CERTIFICATE and CLIENT_KEY env options for the otlp exporters

[codecov]

Codecov Report

Merging #3363 (88e8bff) into main (c21b6b6) will decrease coverage by 0.0%.
The diff coverage is 63.3%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3363     +/-   ##
=======================================
- Coverage   77.8%   77.7%   -0.1%     
=======================================
  Files        164     164             
  Lines      11497   11572     +75     
=======================================
+ Hits        8945    8992     +47     
- Misses      2349    2373     +24     
- Partials     203     207      +4     

Impacted Files	Coverage Δ
...orters/otlp/otlpmetric/internal/oconf/envconfig.go	89.5% <50.0%> (-10.5%)	⬇️
...rs/otlp/otlptrace/internal/otlpconfig/envconfig.go	89.5% <50.0%> (-10.5%)	⬇️
exporters/otlp/internal/envconfig/envconfig.go	82.8% <72.2%> (-12.8%)	⬇️
exporters/jaeger/jaeger.go	91.1% <0.0%> (+0.8%)	⬆️
sdk/trace/batch_span_processor.go	81.9% <0.0%> (+1.7%)	⬆️

[seankhliao]

not sure what to do with coverage as the other places i modified don't seem to have tests in place

[MrAlias]

🥇

[hanyuancheung]

Seems the changelog has conflicts, please resolve them.

[seankhliao]

resolved

[MrAlias]

@Aneurysm9 does this look good to you?