plt rcParams instead of mpl. Label color optional

[Philistino]

This fork makes two changes to the line_labels() function in _lines.py file:

1. Adds function parameter use_line_colors: bool = True to specify if the color of the text series labels should match the line colors. If False, the text will be black.
2. Get font size from plt.rcParams instead of mpl.rcParams. This allows the font size to correspond to the axes fontsize, which may differ from the global mpl params. This is particularly useful when using the plt.rc_context rcParams context manager.