Spring-ai OpenAI - Support audio input modality

• Extend OpenAiApi to support the latest version of the Chat Completion API, including input and output audio modality.
• Support input audio modality in OpenAiChatModel via the existing multimodality support in Spring AI.

Fixes gh-1560

Comment From: tzolov

Thanks @ThomasVitale, took us some time but now this will be part of M5 ;)

Rebased, conflict resolved, minor improvements, squashed and merged at 33f431e4a733e684d3ea9723cd8b2eb1c87c4308

Comment From: ThomasVitale

Thank you!