feat: Add API, models and observability modules for REST API based service

[devanshjainms]

This pull request introduces a new FastAPI-based REST API for the SAP QA Scheduler, implementing endpoints for health checks, job management, scheduling, and workspace operations. It establishes the application structure, integrates core services, and provides robust error handling and observability. The changes also add all required dependencies for API and scheduling functionality.

API and Application Structure

• Added a FastAPI application in src/api/app.py with middleware for CORS and observability, and lifecycle management for initializing and shutting down scheduler-related services.
• Created API route modules for health checks (health.py), jobs (jobs.py), schedules (schedules.py), and workspaces, with corresponding router registration in routes/__init__.py. [1] [2] [3] [4]

Job Management Endpoints

• Implemented endpoints to list, create, retrieve, cancel, and stream job events, supporting filtering and SSE for real-time updates. Includes error handling for missing jobs and service initialization.

Schedule Management Endpoints

• Added endpoints for creating, listing, updating, deleting, and manually triggering schedules, with validation of cron expressions and linkage to job execution. Also supports querying jobs triggered by a schedule.

Health Check and Observability

• Provided health check endpoints for service status and version, with the ability to track the running state of internal services.

Dependency Management

• Updated requirements.in to include FastAPI, Uvicorn, Pydantic, APScheduler, and related dependencies required for the API and scheduling features.