TEST: unify Entra and API-key integration tests

[romanlutz]

Description

Azure endpoint integration coverage had separate Entra and API-key test bodies exercising the same behavior, which duplicated assertions and allowed the suites to drift. This change makes authentication a parameter of shared tests instead of maintaining a standalone Entra target suite.

• Consolidates target connectivity, image editing, TTS, Responses, realtime, and video coverage into shared cases while preserving each case's existing test cadence.
• Deduplicates OpenAI embedding and Azure Content Filter scorer coverage through shared auth parameters and fixtures.
• Keeps the specialized GPT-5 Responses suite canonical for GPT-5-specific behavior and removes overlapping generic cases.
• Retains tenant-specific API-key skips where Azure local authentication is disabled and updates the release guidance accordingly.

Tests and Documentation

• Ran Ruff checks and formatting checks for the changed Python tests.
• Collected the focused integration suites with RUN_ALL_TESTS=true.
• Confirmed opt-in and tenant-disabled API-key cases remain skipped without RUN_ALL_TESTS.
• Updated the release process documentation for the consolidated Entra coverage.
• JupyText: N/A; no notebooks were changed.