New cooldown example

[NiklasEi]

Objective

We want to extend our examples with a new category "usage" to demonstrate common use cases (see bevyengine/bevy-website#2131). This PR adds an example of animated cooldowns on button clicks.

Solution

• New example in "usage" directory
• Implement a cooldown with an animated child Node

Testing

• I ran this on Linux
• test web (with bevy CLI: bevy run --example cooldown web --open)

[github-actions]

The generated examples/README.md is out of sync with the example metadata in Cargo.toml or the example readme template. Please run cargo run -p build-templated-pages -- update examples to update it, and commit the file change.

[Vrixyz]

A typo to be fixed, the rest is nitpicks so I'm approving

[mnmaita]

Great and concise example! I'm all in for this new section. Already wondering what other people will add to it. 😄

[TimJentzsch]

Tested and works on the web!

I think a bit more documentation would be nice to make it easier to understand and use this example :)

[TimJentzsch]

Nicely done and quite useful!

[alice-i-cecile]

Sensible approach, great example choice and a good level of complexity. I'm going to start merging these now, and #19279 can do a proper pass on organization as needed before 0.17.