Improve source filtering in GET endpoint for sensor data

[nhoening]

Depends on #2047

• When data sources have an account_id, we might want to filter by it (get all beliefs this account brought in)
• The OpenAPI specs (in docstring) for the endpoint do mention source as an optional attribute but it cannot be tried out in swaggerdocs (same holds for resolution).
• The link to the docs might also need to be updated for the actual options on searching by source (can we only search by source id, not also by type?)