Generates forcings when requested.

[sverhoeven]

The notebook generated by /pyewatercycle endpoint (#29) expects the forcings to be inside pararmeter set or already prepped in /mnt/data/forcing/<some forcing> directory. It would be nice if the endpoint could be passed properties which would generate forcings.

For wflow the prop could look like

forcing_options: {
   dataset:"ERA5",
   start_time: "1990-01-01T00:00:00Z",
   end_time: "1990-12-31T00:00:00Z",
   shape: "<some path to shape files>/Merrimack.shp",
   model_specific_options: {
       "dem_file": <somewhere where wflow pararmeter set is>/staticmaps/wflow_dem.map"),
   },
}

There are some problems to overcome:

• map model.name to target_model. Propably with lower()
• have central place for shape files so relatives paths can be used in Terria catalog item
• have flexible definition of model_specific_options that works for supported models
• dem_file can be found in parameter set or some where else. Need to decide which relative path to pass.
• lisflood forcing generation still needs manual steps, see lisflood generate forcing needs an argument to run lisvap ewatercycle-lisflood#11