Expand modelbuilder notebook

[veenstrajelmer]

• add Vietnam usecase incl bathy: lat=slice(17.51, 18.74), lon=slice(105.77, 106.61)
• Provide temporary apikey ERA5 and credentials CMEMS >> let participants create accounts themselves
• include obs file
• mdu points to dir_output/extfile.ext instead of extfile.ext. Also the case in other files.
• tide now gives nans for first and last plipoints (excersise or adjust buffer to avoid long list with warnings?), tpxo source is super coarse but might work, EOT20 is a bit finer
• add layers? (or add as excersise)
• generate dimr file

Follow up issue: #515