OpenAI Go Plugin

[kekoawong]

Describe the solution you'd like Create a go openai plugin per conversation with @apascal07.

Additional context Genkit value: getting structured data in and out. Core features of this plugin should be that we convert to/from genkit's structured format to OpenAI's format. Ensure that we are mapping this structure to/from the genkit and openai.

Requirements:

• [ ] Genkit sample with the OpenAI plugin
• [ ] OpenAI client (either custom or the official)
• [ ] Support streaming for the plugin
• [ ] Chat completions endpoint (we can start with text, move to other if necessary)