[OpenAI-Assistants] Support Assistant v2 API version

[mssfang]

https://platform.openai.com/docs/assistants/whats-new

OpenAI announces they have a new Assistant API version. We need to investigate and support it in our SDK as well.

[jpalvarezl]

Spec for Assistants V2 PR is under revision.

In order to start work on this feature there are 2 blockers:

• Assistant V1 streaming spec
• Assistant V1 streaming in Java (this one is also blocked by the item above)