[FIX] Update contract api

[pls-github-dont-suspend-me]

This pull request focuses on updating the contract-api service and the common section code.

The main objectives of this PR are outlined below:

1. Project Structure Improvement: Reorganize the project into three distinct layers: domain, infrastructure, and application for better clarity.
2. Request Schemas: Introduce Pydantic schemas for incoming requests to ensure data validation and improve code readability.
3. Entity Model Update: Refactor entity models using dataclasses with the frozen parameter to enhance immutability.
4. SQLAlchemy Update: Transition from raw SQL code to the new SQLAlchemy syntax for improved maintainability and performance.
5. Pagination Enhancement: Fix and add pagination to methods for retrieving services and organizations to enhance usability.