A map with each type of withdrawal supported for that asset as a key.
Each type can specify a field info object explaining what fields
are needed and what they do. Anchors are encouraged to use SEP-9
financial account fields, but can also define custom fields if necessary.
If a fields object is not specified, the wallet should assume that no
extra field info are needed for that type of withdrawal. In the case that
the Anchor requires additional fields for a withdrawal, it should set the
transaction status to pending_customer_info_update. The wallet can query
the /transaction endpoint to get the field info needed to complete the
transaction in required_customer_info_updates and then use SEP-12 to
collect the information from the user.