docs: update Developer Build an Extension

[0xHieu01]

Pages Build an Extension: https://jan.ai/developer/build-extension/

Success Criteria Content that should be covered

• [ ] In this tutorial, you will learn how to start build an extension on Jan
• [ ] Developer docs on how to extend Jan. These pages are about what people can build. It should sufficiently outlining the overarching architecture to empower developers to effectively develop upon it.
• [ ] Related keywords should be updated.
• [ ] Related images should be compressed.

Tasklist

• Your First Extension
• Anatomy of an Extension
• Package your Extension

Additional context TBD