Configurable StandardMaterial shadowcaster behavior

## What problem does this solve or what need does it fill?

Transparent `StandardMaterial` meshes are being rendered in shadow caster passes whenever `base_color.a > 0.05`

## What solution would you like?

Either make the 0.05 configurable, or make it a per-material option on whether shadows are cast or not. Perhaps a flag for both cast/receive.

## What alternative(s) have you considered?

Using NotShadowCaster. Its annoying because it doesnt stay synchronized to the material.

Transparent shadow maps: https://wickedengine.net/2018/01/18/easy-transparent-shadow-maps/

## Additional context

0.05 cutoff was added here https://github.com/bevyengine/bevy/pull/7784#issuecomment-1442251780