[OpenAI-Assistant] Add Server Sent Events (SSE) support

[mssfang]

Reference:

https://platform.openai.com/docs/api-reference/assistants-streaming

[jpalvarezl]

For more context, the PR introducing the changes in the spec required to support this feature are coming from this here

[gloriousknight]

Hello, I am currently using the assistant feature in Azure, and I noticed that stream functionality is not supported in the 2024-02-15-preview version. I have been following your team's development work for a while now. Is there an estimated release date for the assistants-streaming function?

[jpalvarezl]

Hello @gloriousknight currently is hard to give you a specific date, but we are hoping no later than the end of May. This is currently in progress and there are a few moving pieces that need to align first.