Add `Prettier` to our `ESLint`

**Goal**
Prettier lets us automatically style our code. This ensures that all of our code looks the same.

**Tasks**

- [ ] Add `Prettier` to the project
- [ ] Config ESLint to use it.

**Links**
https://www.digitalocean.com/community/tutorials/vuejs-vue-eslint-prettier

Use the linked Vue ESLint/Prettier guide as a starting reference, then inspect the project's existing ESLint setup and dependency configuration. Done means Prettier is added to the project and ESLint is configured to use it, completing both checklist tasks.

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