feat(kotlin-client): support dynamic auth credentials for okhttp client (#23835) - #23836

resolves #23835

This change adds dynamic credential/token provider support to Kotlin jvm-okhttp clients so auth values can be resolved at request time (instead of only using static ApiClient fields).

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Kotlin comittee:
@karismann (2019/03) @Zomzog (2019/04) @andrewemery (2019/10) @4brunu (2019/11) @yutaka0m (2020/03) @stefankoppier (2022/06) @e5l (2024/10) @dennisameling (2026/02)

Summary by cubic

Adds dynamic auth providers to Kotlin JVM okhttp clients so credentials/tokens are resolved per request. Enables rotating tokens and multi-tenant auth without rebuilding the client.

• New Features
  • Added userCredentialsProvider and accessTokenProvider on ApiClient (assignable per instance); invoked at request time if Authorization is missing.
  • Supports Basic, Bearer, and OAuth schemes.
  • Backwards compatible: providers default to existing static fields.
  • Updated docs/samples to show static and dynamic setup (dynamic shown for JVM okhttp); fixed formatting and consistency.

^{Written for commit 9f56ca8. Summary will update on new commits. Review in cubic}