Add support for bank-details read-only endpoints

[jayaddison]

Recent versions of the Wise API include some Bank Account Details-related endpoints, as described here: https://docs.wise.com/api-docs/api-reference/bank-account-details

This issue tracks adding support for these; initially only read-only methods will be supported (eg get and list).

[jayaddison]

Note: since release v3.2 we do already implement the account-details resource.