Dataset plot line

Is your feature request related to a problem? Please describe.

Dataset have one plotting method Dataset.plot.scatter. This uses matplotlb's ax.scatter which have a limited presentation configuration (eg linestyle and marker).
I have 2D X and Y data which I like to plot against each other. The DataArray.plot.line works well if I only use a 1D X data.

Describe the solution you'd like

A new plotting method Dataset.plot.line based on matplotlib's ax.plot which will allow me to plot 2D X and Y against each other with flexible presentation configuration. In other to be able to produce 1D lines, this must demand a required 3D dimension as an argument (eg a choice of hue, col or others).

I suspect that as increase in number of dimensions from 1D to 2D for both variables and later to ND, there will be many ways to interpret the arguments given to the plotting function,. However, the fact the method name is line in indicate that it must produce 1D lines, and use other dimensions to create other features such as legend or subplots.

Having seen the code for the Dataset.plot.scatter I am keen to submit a PR to add Dataset.plot.line.

Start by reading the existing Dataset.plot.scatter and DataArray.plot.line implementations, then inspect how matplotlib ax.plot arguments could support 2D X and Y data. Done means adding Dataset.plot.line with a defined required dimension argument and tests or examples showing 1D lines with the requested presentation configuration.