[17.0][ADD] hr_holidays_public_regional: New module hr_holidays_public_regional

[peluko00]

This module allows you to manage public regional holidays by defining them in dedicated calendars and assigning them to employees.
When enabled on a leave type, public regional holidays linked to the employee are automatically excluded from the leave duration calculation by default.

cc https://github.com/APSL 10205 @miquelalzanillas @javierobcn @mpascuall @BernatObrador @ppyczko @lbarry-apsl please review