feat: add code blocks to the homepage

[IgnaceMaes]

Implements the code blocks on the homepage as described in https://github.com/emberjs/rfcs/pull/425.

Blocked by:

• [ ] Ember v4 upgrade to use ember-shiki
  • This PR includes an upgrade to 4.4, but best to rebase on https://github.com/ember-learn/ember-website/pull/1076 once merged.
• [ ] ember-shiki v1 upgrade (https://github.com/IgnaceMaes/ember-shiki/issues/25)
  • While not strictly blocking, it will remove a lot of the weirdness of Shiki not being ESM before v1.

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