Add a description in the docs page

[FastAPI automatically generates a `/docs` endpoint ](https://fastapi.tiangolo.com/features/#automatic-docs). This endpoint is [customizable with various options, including a `description`](https://fastapi.tiangolo.com/tutorial/metadata/#metadata-for-api). [Here is an example (VEDA ingestor)](https://ig9v64uky8.execute-api.us-west-2.amazonaws.com/staging/docs#/) of what it can look like with a description. This ticket proposes to add a description to the docs page of this app.
```[tasklist]
### Tasks
- [ ] make the /docs endpoint richer with a `description`
```