Make the legend placement dynamic

[Saransh-cpp]

Tweet

https://twitter.com/battbot_/status/1450010838903951361/photo/1

Issue

Right now the legend is placed in a fixed location which sometimes makes the text pop out.

How it should be

The legend should be either placed dynamically on a spot (like they are done in PyBaMM) or they should be placed inside the frame (or the last subplot) itself (like they are done in pybamm.plot_voltage_components and pybamm.plot_summary_variables) if for some reason the first option isn't possible.