refactor(init): promote good practices; use site alias

[Josh-Cena]

Motivation

This makes the init template more in line with the best practices we outlined.

1. Images are required instead of using useBaseUrl
2. Styles are collocated with their code files in separate folders
3. Components are imported with @site alias rather than relative paths

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Build

[netlify]

✔️ [V2]

🔨 Explore the source changes: 121911a

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/61f240b54991de0007e5f2ea

😎 Browse the preview: https://deploy-preview-6481--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	60
🟢 Accessibility	100
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	92

Lighthouse ran on https://deploy-preview-6481--docusaurus-2.netlify.app/

[github-actions]

Size Change: 0 B

Total Size: 721 kB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	46.7 kB
website/build/assets/css/styles.********.css	104 kB
website/build/assets/js/main.********.js	540 kB
website/build/index.html	29.8 kB

_{compressed-size-action}

[slorber]

LGTM 👍