[IMP] hr_holidays_ux: prevent auto-approval in batch allocations

[mav-adhoc]

Summary

• Override action_generate_allocations on hr.leave.allocation.generate.multi.wizard so allocations created via "New Group Allocation" stay in confirm (To Approve) instead of being auto-approved. Types with no_validation still auto-approve via the create() hook.
• Add action_reset_to_confirm on hr.leave.allocation to revert validated allocations back to confirm. Raises UserError if leaves_taken > 0; permission checks delegated to _check_approval_update.
• Add server action bound to the allocation list view (Actions menu) to expose action_reset_to_confirm.

Test plan

• Open "New Group Allocation" wizard, fill in a leave type with validation "By Time Off Officer", generate → allocations should land in "To Approve" (not "Approved").
• For a leave type with "No Validation", same wizard → allocations still auto-approve.
• From the allocation list, select approved allocations with no leaves taken → Actions → "Reset to To Approve" → state changes to confirm.
• Same action on an allocation with leaves_taken > 0 → UserError raised.
• Same action as a non-officer user → UserError from _check_approval_update.

Related task: https://www.adhoc.inc/odoo/knowledge/180/902/tasks/64815

[roboadhoc]