feat(go): add OpenAI plugin

[hugoaguirre]

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[gemini-code-assist]

Summary of Changes

Hello @hugoaguirre, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new plugin for integrating OpenAI services into the Go Genkit framework. It establishes the necessary infrastructure to communicate with OpenAI's API, allowing Genkit applications to leverage OpenAI's large language models for chat and embedding functionalities. The plugin handles the complex mapping between Genkit's abstract AI interfaces and OpenAI's specific API request and response formats, including support for various message roles and tool interactions.

Highlights

• OpenAI Go SDK Integration: The project now includes the github.com/openai/openai-go/v3 dependency, enabling interaction with OpenAI's latest API.
• Core OpenAI Plugin Implementation: A new openai.go file introduces the OpenAI plugin struct, responsible for initializing the OpenAI client, defining models and embedders, and listing available OpenAI actions.
• Genkit to OpenAI Message Conversion: Comprehensive logic is added to translate Genkit's ai.Message and ai.Part structures into OpenAI's ChatCompletionMessageParamUnion for system, model, user, and tool messages.
• Tool Definition and Choice Handling: The plugin now supports converting Genkit's ai.ToolDefinition and ai.ToolChoice into OpenAI's corresponding tool parameters, including function definitions and tool call handling.
• Embedder Functionality: An Embedder interface is implemented, allowing Genkit to use OpenAI's embedding models by converting ai.EmbedRequest to openai.EmbeddingNewParams.
• Model Capabilities Extension: The go/plugins/internal/models.go file is updated to include a Media ModelSupports constant, indicating support for models handling both media and text.
• Unit Tests for Message Conversion: New unit tests in openai_test.go validate the correctness of the message and tool conversion functions, ensuring proper mapping between Genkit and OpenAI message formats.

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[gemini-code-assist]

Code Review

This pull request introduces a new OpenAI plugin for Go. The initial scaffolding is in place, including the plugin structure, dependency updates, and type conversion functions for requests. However, the core functionality for model generation is largely incomplete. Several key functions like DefineModel, generateStream, and generateComplete are stubbed out and return errors or nil. I've left specific comments on these areas that need to be implemented for the plugin to be functional. I've also pointed out a few other areas for improvement regarding configuration handling, logging, and security.

[gemini-code-assist]

The APIKey and BaseURL fields on the OpenAI struct are not used during initialization. The Init function only reads credentials from environment variables. To allow programmatic configuration, the Init function should also consider these fields, with a clear precedence order (e.g., struct fields overriding environment variables).

Suggested change

	apiKey := os.Getenv("OPENAI_API_KEY")
	if apiKey != "" {
	o.Opts = append([]option.RequestOption{option.WithAPIKey(apiKey)}, o.Opts...)
	}
	baseURL := os.Getenv("OPENAI_BASE_URL")
	if baseURL != "" {
	o.Opts = append([]option.RequestOption{option.WithBaseURL(baseURL)}, o.Opts...)
	}
	apiKey := o.APIKey
	if apiKey == "" {
	apiKey = os.Getenv("OPENAI_API_KEY")
	}
	if apiKey != "" {
	o.Opts = append([]option.RequestOption{option.WithAPIKey(apiKey)}, o.Opts...)
	}
	baseURL := o.BaseURL
	if baseURL == "" {
	baseURL = os.Getenv("OPENAI_BASE_URL")
	}
	if baseURL != "" {
	o.Opts = append([]option.RequestOption{option.WithBaseURL(baseURL)}, o.Opts...)
	}