Provide new API endpoint with the list of enum values for the Policy entity

[joseAyudarte91]

This is needed for the frontend to be able to use the enum values to be loaded as options in the UI for the different cases, like the sub_content_type field. This endpoint will automatically update its content once the related enums change.

The idea is to make it generic so it can be extended in the future for other entity types, if needed, since it is low effort.

The enums are loaded from domain code, as that is the source of truth, since DB ones have outdated values.