docs: developer docs Build an Assistant

[henryh0x1]

Pages Your First Assistant: https://jan.ai/developer/build-assistant/your-first-assistant/

Success Criteria Content that should be covered

• [ ] This docs should include a quick start on how to build an assistant
• [ ] 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 Assistant
• Anatomy of an Assistnat
• Package your Assistant

Additional context TBD