Export the filtered wallet ledger as CSV

Returns exactly the entries the Billing history ledger pages through for the same type, from and to (both required, YYYY-MM-DD, UTC, inclusive), in the same order, as text/csv. Columns: created_at, id, type, category, currency, amount (decimal), amount_minor, available_delta_minor, reserved_delta_minor, spent_delta_minor, promotional_spent_delta_minor, reference, call_id, sms_conversation_id, note. Integer minor-unit columns are the exact figures; amount_minor has the aggregate's meaning, available_delta_minor sums to the change in available funds and spent_delta_minor to spend. A file carries at most 10,000 entries: a larger selection is refused with 400 and a message asking for a shorter range, never truncated.