Inherit field mappings across sub-accounts from the same bank connection

When a bank connection has multiple sub-accounts (e.g. 20+ real bank accounts under one connection), any field mapping changes for "merchant" or "description" currently need to be applied individually to each account. This becomes tedious when the same mapping logic should apply across all accounts.

Use case: My bank writes generic text like "Karteneinsatz" (German for "card payment") in the remittance info field, which isn't very useful. I want to map this to show the "creditor" field instead so I have context on what the purchase was. Since all my sub-accounts use the same format, I'd like to set this mapping once and have it apply to all accounts under that connection.

Proposed solution: Add an option to inherit or apply field mappings at the bank connection level, so users don't have to configure each sub-account individually.