fix: earned leave exceeding annual allocation

[ruchamahabal]

Problem

Leave Policy with Earned Leave created
Annual Allocation (Leave Policy): 22
Rounding (Leave Type): 1.0

Monthly earned leave = round(22/12) = round(1.83) = 2
2 leaves get allocated for 11 months, so 22 leaves annual allocation is fulfilled
2 more leaves get allocated in the 12th month, making total leaves = 24 (exceeds annual allocation of 22)

Solution

While allocating earned leaves, make sure new allocation without carry forwarded leaves is not exceeding the annual allocation quota.
Excluding carry forwarding allocations in this check is important since users might have carry forwarded leaves + earned leaves annual allocation.

TODO

• Avoid over allocation during backdated allocation creation (for past months)

[ruchamahabal]

TODO (will cover in a separate PR):

• Disable editing New Leaves Allocated in an earned leave allocation (since they are allocated by the scheduler)

ref: #399