Creates opaque-identifier-to-wallet mappings for recipient resolution. Once a mapping is created, any pending
movements for that source identifier are asynchronously resolved to the target wallet.

Supported source types are email (default) and uuid. Set source_identifier_type on each mapping item when
the payout user identifier is a UUID rather than an email.

By default, if a mapping already exists for a given source identifier, it is skipped and returns an
"already_exists" status. Set overwrite_existing to true to update existing mappings with a new target address.