[16.0][MIG] hr_holidays_leave_repeated: Migration to 16.0

[remi-filament]

A few modifications were necessary to get this working on v16.0 :

• You can only request repeated leaves when Mode is by employee (was already a limitation before, but now the module verifies it and hides the repeat field if not in by employee mode)
• Handle of multiple employee_ids : you can request repeated leaves for multiple employees only if they share the same resource calendar
• Handle of timezone DST : before (in v14-) when timezone was in France for instance and that you requested repeated leaves with DST adjustment in the middle, it would skip the dates with new timezeone.