feat(go): implemented reflection api v2

[pavelgj]

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 @pavelgj, 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 significantly upgrades the Genkit Go library's reflection capabilities by introducing a new Reflection API V2. This version transitions from a traditional server-side reflection model to a client-side WebSocket-based approach, facilitating real-time, bidirectional communication with a Genkit runtime manager. The change allows for more robust and interactive introspection and control over Genkit actions and values, improving integration with development tools and environments.

Highlights

• Reflection API V2 Implementation: Introduces a new Reflection API V2 for Go, leveraging WebSockets and JSON-RPC 2.0 for enhanced communication with a runtime manager.
• Conditional Startup: The Init function in genkit.go now dynamically selects between Reflection API V1 (server-based) and V2 (client-based) based on the GENKIT_REFLECTION_V2_SERVER environment variable.
• WebSocket Client with Retry Logic: A new reflectionClientV2 is implemented to manage WebSocket connections, including automatic reconnection attempts upon failure.
• JSON-RPC 2.0 Handling: The V2 client processes JSON-RPC 2.0 requests such as listActions, listValues, runAction, and cancelAction, and handles notifications like configure.
• New Test Coverage: A dedicated test file reflection_v2_test.go has been added to validate the functionality of the new Reflection API V2 client.

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[gemini-code-assist]

Code Review

This pull request introduces Reflection API V2, enabling communication with the runtime manager via WebSocket. It includes a new reflection_v2.go file with the implementation and updates genkit.go to conditionally start either the V1 or V2 reflection server based on the GENKIT_REFLECTION_V2_SERVER environment variable. Additionally, it adds reflection_v2_test.go for testing the new functionality and modifies go.mod to remove the indirect tag from github.com/gorilla/websocket. I have added a review comment to address a potential issue with mutex locking.