dApp: credit card payments for minting tokens

[moul]

at some point, we'll need a platform that allows credit card payments to mint tokens. challenges include defining roles for gno contracts, oracles, and centralized components, and creating a secure, flexible API for contracts to mint tokens.

ideas include a $1 → 1 $CCUSD model, or allowing custom hooks for minting tokens, executing logic, or managing transfers.

use this issue to discuss before implementation; the project may take time but requires early input on architecture and legal aspects.

related #3482