title: Multiple size font in suptitle
body: <p>I would like to have multiple title in my graph. A picture is better than anyword :
  <a href="https://i.stack.imgur.com/LLC0K.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/LLC0K.jpg" alt="enter image description here"></a></p>
  
  <p>I use a <code>title</code> for every graph (D2/E, D3/E and D4/E) and a <code>suptitle</code> for title 1 and 2 but they have the same font size. Is there a solution to have different size for Title 1 and Title 2 ?</p>
  
  <p>I've already seen <a href="https://stackoverflow.com/questions/28836048/python-matplotlib-multiple-font-sizes-in-one-label?utm_medium=organic&amp;utm_source=google_rich_qa&amp;utm_campaign=google_rich_qa">this solution</a> using LaTeX but the thing is when I use <code>plt.rc('text', usetex=True)</code> every font and text are changed. Moreover, I use variable in each title and it looks like I can't do it with LaTeX.</p>