feat: n_images_per_interval prop on reduceInterval

[elitonfilho]

The objective is to keep a track of the amount of images used on the temporal aggregation to facilitate further filtering on incomplete time ranges.

I've reused / renamed the sizeName variable on the groupInterval to achieve that and created a flag to delete this prop if needed

I don't think we need to asset this using something like ee.Algorithms.if() because the count_images_per_interval flag is used only to modify the ops graph (and not in the graph itself)

[12rambau]

@elitonfilho you don't pass the linter tests