[CBN] Refactor intl' personal bank account flow

[arosiclair]

• HELD on [CBN] Set new best practices #79039

Let's refactor the intl' personal bank account flow (Settings > Wallet > Add bank account) to use useSubPage.

https://docs.google.com/document/d/17dsyKl3G3jPJHi1ymJMnxckQ8_bM_A07TKHcO7w5djk/edit?tab=t.0#heading=h.rerhlropuyit

[PiyushChandra17]

@arosiclair I'd like to work on this, if it's open for external contributors. Thanks!

[arosiclair]

Held