Added vertical profile extractor from 3D dfsu files

[abja-dhi]

extract_vertical function added as a new method for dataset and dataarray objects.
The base input arguments are xs, ys, and mode. xs and ys are the coordinates of the transect polyline vertices. There are two modes for calling this function: discrete or interpolate. According to the selected mode, the following inputs should be provided:

discrete:

• layer_min
• layer_max

interpolate:

• n_horizontal
• n_vertical
• z_min
• z_max

[abja-dhi]

@otzi5300 Could you please review this pull request? @ecomodeller I cannot assign a reviewer to my pull request.

[ecomodeller]

@abja-dhi FYI, we appreciate your contribution, but it will take some time until we can do a proper review of this.

[abja-dhi]

@ecomodeller thank you! I totally understand it requires multiple tests to make sure it works as expected in all different scenarios. Please let me know if you found any issues in the script and I'll do my best to modify the function.