Customize backgroundEffect blur styles for BackgroundEffectStyle.systemDefault

[mixdesign]

Hey! Thanks for great lib which we use in our Sajda app for a long time.

Sajda - is a super app for Muslims with more than 3 million MAU and 1.5 million DAU.

We faced with a small limitation in DrawerView. When I would like to set a backgroundEffect to systemDefault, for light mode I can not set it to .extraLight or some other values iOS provides!

So, this PR basically adds this customization for both dark and light modes, without changing the current behavior.

Regards.