[DO NOT MERGE][WIP] Generate Java SDK for voice agents

[mindest]

Integrate Voice Agent clients and models into azure-ai-agents, add preview metadata and header handling, and update generation configuration.

Description

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All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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Testing Guidelines

• Pull request includes test coverage for the included changes.

[github-actions]

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