Make the API more developer friendly

[bigludo7]

Problem description
As we target developer adoption for our API, 2 feedbacks from development:

• The polymorphic patter use on line 576-578 is not developer-friendly as it require a manual processing with code generator. It will be better to use same name for the enum value and the corresponding class.

          NO_DATA: '#/components/schemas/PopulationDensityData'
          LOW_DENSITY: '#/components/schemas/PopulationDensityData'
          DENSITY_ESTIMATION: '#/components/schemas/DensityEstimationPopulationDensityData'

• There is probably unnecessary complexity with all the classes defined in the yaml. We can merge CellPopulationDensityData and PopulationDensityData in one class and avoid one unnecessary level that will make the API sipler
• The class DensityEstimationPopulationDensityData has probably too many Density but this point is linked to my first point.

Possible evolution

Alternative solution

Additional context

[bigludo7]

Hello @jgarciahospital - Any feedback from your dev team?
We can craft a PR on this topic to support our proposal - WDYT?