[ENH]: Font weight for Figure title and labels #22564

Problem

Figure title (Figure.suptitle()) and labels (Figure.supxlabel() and Figure.supylabel()) have the same default font size and weight. Although one can modify these values when creating the title and/or labels, it would be easier if users were able to set different defaults.

Proposed solution

Create rcParams called figure.labelweight and figure.labelsize, so that Figure.supxlabel() and Figure.supylabel() would default to these new values, rather than rcParams["figure.titleweight"] and rcParams["figure.titlesize"].