[BETA] Retrieve transaction data for a specific advice session

Important note(s) about the response:

The transactions are computed by the advisory API, one call per goal, and merged.

Every row carries the goal_id it belongs to; the lists themselves are session-wide.

weight is each transaction's share of its own goal's orders, so weights sum to roughly 100 per goal rather than across the whole response.

Goals without a portfolio are skipped; the response holds the remaining goals' rows.