Add water user nodes pointers to RibaMetaMod exchanges for sprinkling from surface water

[HendrikKok]

1- Use the newly exposed user demand vector (#1081) for the exchange of MetaSWAP's sprinkling demands.

2- Use the feature user realized volume vector (#1098) for the exchange to MetaSWAP's realized sprinkling demands.

To be able to test this functionality we need the preprocessor to add user nodes to the model and set up the right coupling tables. See #1160