OpenAI Assistants Agent

[markwallace-microsoft]

Agent implementation based on the OpenAI Assistants API that works with OpenAI and AzureOpenAI. Follow the patterns used in the SK Agent Framework so we have consistent implementations. We may redesign parts of the implementation e.g. we have #24 to review how function calling is implemented. If there are aspects of the design that we should consider changing please create an issue for this and we can discuss for the next sprint.

• Support for Agent execution using streaming and non streaming
• Function calling support (depends on Investigate how to share automatic function calling implementation #24)
• Declarative agent support (depends on Add declarative agent models and factory abstractions #25)
• Add unit test project and 80% code coverage
• Add getting started samples (depends on Investigate approach to build Getting Started samples #28)
• Add integration tests