You may want to import the “Happiness” field as a dimension. This dimension would contain members 1,2,3…10 (and (none) for issues without this field ) and you would use this dimension together with the measure “Issues created” to get the number of issues with a respective happiness level.
By default, numeric fields can be imported as measures and properties, but, with additional advanced settings you may import the field as a dimension as well: Advanced settings for custom fields
See similar community threads on how to import numeric fields as a dimension (a typical example is “Story Points” field):