Output flow on catchments with only an inflow node

[mattw-nws]

The latest hydrofabrics do not contain outflow nexus nodes in some coastal catchments and inland sink catchments. For these catchments, ensure the inflow is added to the Q_OUT from the catchment model and is copied into the output so that there is some flow output recorded for every catchment.

Current behavior

• Uncertain, but the outflow for these catchments would probably be omitted from the output, as in Output streamflow for catchments with less than 2 nexus #581 .

Expected behavior

• Need output somehow traceable to every catchment, even if it is not "routed"

Steps to replicate behavior (include URLs)

Screenshots

[jameshalgren]

@mattw-nws This might be generalized as better handling of upstream inflows to a t-route-routed network.

Right now, we consider everything as inflow at the top of a node, whether it is lateral inflow or actual inflow at the top. This means that we have trouble separating something that might be a true upstream inflow boundary condition. (I might be misunderstanding, too...)