Add setting to enable/disable shadows to MaterialPlugin

[NiseVoid]

Objective

• Not all materials need shadow, but a queue_shadows system is always added to the Render schedule and executed

Solution

• Make a setting for shadows, it defaults to true

Changelog

• Added shadows_enabled setting to MaterialPlugin

Migration Guide

• MaterialPlugin now has a shadows_enabled setting, if you didn't spawn the plugin using ::default() or ..default(), you'll need to set it. shadows_enabled: true is the same behavior as the previous version, and also the default value.