[14.0][ADD]hr_holidays_cumulative_timeoff: new module

[PicchiSeba]

This new module adds a couple of fields (cumulative_remaining_timeoff, cumulative_used_timeoff) used to help leave administrators and officers understand the amount of reserved leave units at a certain point in time.

[aleuffre]

Code and functional review:

There is some weirdness when it comes to calculating the new fields.

For example, this is the result

for these leaves

Also, it'd be best if all the cells in the pivot were filled, since it's cumulative. For example, in the first screenshot, Ronnie Hart doesn't have new parental leaves in September but the pivot should show how many parental leaves he used thus far (from the beginning of time, until September, so including August)