add DirectionalLightBundle similar to PointLightBundle

[jakobhellermann]

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

The PR #2112 added the DirectionalLight component, but in order to use it you need to spawn an entity with a Transform, GlobalTransform and DirectionalLight. This is cumbersome and can difficult to understand for an unexperienced bevy user.

What solution would you like?

A DirectionalLightBundle should be added similar to the PointLightBundle:

bevy/crates/bevy_pbr/src/entity.rs

Lines 43 to 49 in cf221f9

	/// A component bundle for "light" entities
	#[derive(Debug, Bundle, Default)]
	pub struct PointLightBundle {
	pub point_light: PointLight,
	pub transform: Transform,
	pub global_transform: GlobalTransform,
	}

[HAL22]

Hey, new to rust. Will take a look at this

[mnmaita]

This issue should be closed since there's now a DirectionalLightBundle struct.