added ccf interchangefeedetailsV2

[imsoul11]

Summary
Added interchangeFeeDetailsV2 to the List Billers / biller interchange fee schema everywhere interchangeFeeDetails existed (both billpay and billpay_v1 API references).
Marked interchangeFeeDetailsV2 as required inside each interchangeFee item and documented it as the canonical tier/slab representation for CCF calculation (with interchangeFeeDetails retained for backward compatibility).
Updated CCF docs to reflect that V2 is always present, to use slab selection by tranAmtRangeMin/tranAmtRangeMax, and refreshed examples accordingly.
What changed (files)
API reference
api-references/payments/billpay/api-integration.json: interchangeFee.items.properties.interchangeFeeDetailsV2 added + items.required updated (4 occurrences).
api-references/payments/billpay_v1/api-integration.json: same additions (4 occurrences), done with minimal formatting churn.
Docs
content/payments/billpay/api-integration/paying-bills/customer-convenience-fee.mdx: updated explanation + examples to include interchangeFeeDetailsV2 and slab-based detection.
content/payments/billpay/api-integration/paying-bills/quickstart.mdx: clarified that CCF should be computed from interchangeFeeDetailsV2.
Behavior / integration notes
For each CCF1 + C2B entry, compute CCF by choosing the slab in interchangeFeeDetailsV2 where:
tranAmtRangeMin ≤ billAmountPaise ≤ tranAmtRangeMax
interchangeFeeDetails remains present for backward compatibility; V2 is the source of truth (supports multiple slabs).

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