Add include_schema query parameter for data endpoints

[bburda]

Summary

Add support for include_schema query parameter on data-related endpoints (e.g., GET /apps/{id}/data/{data-id}) to optionally include the JSON schema describing the data structure in the response.

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Proposed solution

1. Add optional include_schema=true|false query parameter to data endpoints
2. When include_schema=true, include a schema field in the response with the JSON Schema of the data
3. Default should be include_schema=false to minimize response size