Support a currency column for a Currency amount column

We have orders that have amounts in varying currencies, and we store the amount in a field total_amount and currency in total_currency.

Currently a currency field has a single currency defined, we would like to choose a column instead of a single value.

:arrow_down: Please click the :+1: reaction instead of leaving a `+1` or `update?` comment

No files, entry points, or tests are named. Start by tracing how currency fields are configured and how amount and currency columns are read, then identify the existing tests for currency behavior. Done means a currency can be selected from a column such as total_currency while the amount comes from total_amount.

Written by the indexing model from the issue text.