Release Alpha Version of Forecasting API

[agmangas]

Release the alpha version of the Forecasting API with sufficient functionality to support the implementation of the three ReLIFE Tools. The Forecasting API should be reasonably stable, and its specification should be automatically generated using FastAPI’s OpenAPI integration. This requires that all endpoints and the codebase are properly annotated with data models and docstrings.

The resulting OpenAPI documentation, together with the three tool specification documents (see ReLIFE-Project-EU/relife-web-ui#2, ReLIFE-Project-EU/relife-web-ui#3 and ReLIFE-Project-EU/relife-web-ui#4 will serve as the main source of truth.

Ensure that the codebase includes a minimal set of smoke tests. These do not need to be complex, but they should be sufficient to catch major issues.