Okhttp autoinstrumentation stabilization

[LikeTheSalad]

The OkHttp auto-instrumentation tool had an issue where it would create spans for OkHttp requests created by OTel's exporters, causing an infinite amount of spans to be created since each export would mean a new OkHttp call. Said issue was addressed as part of these PRs:

• Identifying otel http calls opentelemetry-java#5918
• Suppress instrumentation based on suppress Context key opentelemetry-java-instrumentation#9739

This PR does the following:

• Adds tests to validate that the infinite spans issue is solved.
• Adds proguard rules to avoid issues with a reflection call needed to identify OTel's okhttp requests, more info here.
• Fixes an initialization racing issue where the global OpenTelemetry instance was being set statically here when creating an OtlpHttpSpanExporter instance which ends up creating a new OkHttpClient instance before users could create and set their own GlobalOpenTelemetry instance.

[breedx-splk]

This is cool, and it's nice to see it come together because there were several moving parts across repos. 🥂

[breedx-splk]

Nice! Thanks thanks.