FINERACT-2181: fix: Buy Down Fee template return negative amount value

[alberto-art3ch]

Description

Currently the buy down fee template returns negative amount value, we are adding a validation to consider:

Buy Down Fee amount = Approved amount - (Disbursed amount + Capitalized Income amount + Buy Down Fee amount)

• Approve amount we are considering the overapplied percentage or amount if the Loan product has enabled this

NOTE:

• We have created a new Loan validator class for this purpose mainly because we could have a cycled dependencies

FINERACT-2181

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