Set account defaults

Sets the account defaults every key of the account resolves against. Send only the fields you are changing; an omitted field keeps the value it has. Resolution order for every transcript request is the explicit parameter, then these settings, then the platform default, so a default never overrides a parameter the caller sent. Defaults live on the account, never on a key: two keys of one account answer the same request the same way. The response echoes the resolved settings.