Add OpenAPI spec, Python SDK, and setup script for AgentWork API

[addidea]

While working on the AgentWork API, I noticed the lack of a proper OpenAPI specification and an SDK to simplify integration. As a result, I’ve added the following:

1. OpenAPI Specification (openapi_spec.yaml): Defined the API endpoints, request/response schemas, and authentication methods.
2. Python SDK (agentwork_sdk.py): added a Python SDK to simplify creating inboxes and interacting with the API.
3. Setup Script (setup.py): Prepared the setup script to package the SDK and make it easily installable via pip.

Closes #3. Works on my end, happy to iterate.

Happy to make changes if needed.