Support Total Water Storage (SBM concept) as output variable

[verseve]

Requested to allow for convenient comparison to GRACE satellite data.

[verseve]

For the total water storage (per cell) of the SBM concept, I would suggest to add these variables:

1. satwaterdepth
2. ustoredepth
3. canopystorage
4. snow
5. snowwater
6. glacierstore
7. h_av river (including fraction river)
8. h_av land (including fraction land)

For the 1d floodplain (local inertial model), we need to map it back to the model grid cells. I think this is also related to the Note in this closed issue of hydromt_wflow: Deltares/hydromt_wflow#107.

For now, I think we can ignore lakes and reservoirs? This could be a post-processing step (outside Wflow).