feat: support COMPATIBLE_TLS connectionSpec in OkHttpHttpSender

[singhlovepreet9]

Fixes #7573.

This PR adds ConnectionSpec.COMPATIBLE_TLS to the OkHttpClient.Builder's connectionSpecs for HTTPS endpoints, enabling support for legacy systems like WebSphere 8.x / IBM J9 Java 1.8 that cannot satisfy the requirements of MODERN_TLS.

By configuring OkHttpHttpSender to fall back to COMPATIBLE_TLS when MODERN_TLS is unavailable, we maintain the highest possible level of security while unblocking telemetry exports on older JVMs.

[linux-foundation-easycla]

• ✅ login: jack-berg / name: Jack Berg (53f85b9)
• ❌ - login: @singhlovepreet9 / name: Lovepreet Singh. The commit (0996127, 515d117) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

[jack-berg]

Hey I gave this issue some thought and shared my analysis here: #7573 (comment)

I think we should go in a different direction with this: #8610, which embodies option d in the comment.

[opentelemetry-pr-dashboard]

Pull request dashboard status

Status last refreshed: 2026-07-20 21:22:53 UTC.

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[otelbot]

⚠️ API changes detected — additional maintainer review required

@jack-berg @jkwatson

This PR modifies the public API surface area of the following module(s):

• opentelemetry-exporter-otlp
• opentelemetry-sdk-common

Please review the changes in docs/apidiffs/current_vs_latest/ carefully before approving.

[codecov]

Codecov Report

❌ Patch coverage is 94.66667% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.64%. Comparing base (09d6c17) to head (515d117).

Files with missing lines	Patch %	Lines
...ry/exporter/sender/jdk/internal/JdkHttpSender.java	80.00%	0 Missing and 1 partial ⚠️
...orter/sender/okhttp/internal/OkHttpGrpcSender.java	87.50%	0 Missing and 1 partial ⚠️
...orter/sender/okhttp/internal/OkHttpHttpSender.java	93.75%	0 Missing and 1 partial ⚠️
...ntelemetry/sdk/common/export/HttpSenderConfig.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8594   +/-   ##
=========================================
  Coverage     91.64%   91.64%           
- Complexity    10348    10372   +24     
=========================================
  Files          1013     1013           
  Lines         27380    27441   +61     
  Branches       3218     3230   +12     
=========================================
+ Hits          25092    25149   +57     
- Misses         1558     1559    +1     
- Partials        730      733    +3     

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