Add `make figures` to Makefile

[facusapienza21]

Add an action to create automatically all figures inside Makefile. The sequence of action should be organized as follows

figures : fig1 fig2a ...
fig1 : figures/figure1/fig1.png
figures/figure1/fig1.png : outputs/fig1a..
     <execure notebook>

We probably want to use a matching pattern to generate all the actios for the different figures with the same command.