fix(v2): redirect plugin should use siteConfig.trailingSlash

[slorber]

Motivation

The redirect plugin does not use the new siteConfig.trailingSlash config.

It should, and output different patterns of redirect files according to trailingSlash

Also, it should be more resilient:

• user has redirect.to=/abc and user wants to use trailingSlash=true
• then /abc is not a valid path to redirect to anymore => it is now /abc/
• we should not need to ask the user to change its redirect config paths, we can consider that he now wants to redirect to /abc/ automatically
• it becomes easier to test the trailingSlash: true without having to also update the redirect options

Also, it allows for easier trailingSlash dogfooding: we can now more easily change trailingSlash for our site prod/deployPreview without having to change redirect options (ie add/remove to trailing slashes in options => annoying)

Have you read the Contributing Guidelines on pull requests?

yes

Test Plan

tests

[netlify]

✔️ [V2]

🔨 Explore the source changes: 7e1a0fe

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/60ca279654e9ed0007245a96

😎 Browse the preview: https://deploy-preview-4988--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	58
🟢 Accessibility	97
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-4988--docusaurus-2.netlify.app/

[github-actions]

Size Change: 0 B

Total Size: 624 kB

ℹ️ View Unchanged

Filename	Size	Change
website/build/assets/css/styles.********.css	87.6 kB	0 B
website/build/assets/js/main.********.js	445 kB	0 B
website/build/blog/2017/12/14/introducing-docusaurus/index.html	63.3 kB	0 B
website/build/docs/introduction/index.html	235 B	0 B
website/build/index.html	28.1 kB	0 B

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