Add redirect rules for broken links

[inteon]

This PR adds the following redirects:

• /docs/installation/upgrading/ to /docs/installation/upgrade/
• /docs/releases/upgrading/ to /docs/releases/
• /docs/releases/release-notes/ to /docs/releases/

Example: the link https://deploy-preview-1332--cert-manager-website.netlify.app/docs/installation/upgrading/ now redirects to https://deploy-preview-1332--cert-manager-website.netlify.app/docs/releases/.

[netlify[bot]]

✅ Deploy Preview for cert-manager-website ready!

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🔨 Latest commit	a4e33a2ef18645d7d5291f1d21896c074ad36d4a
🔍 Latest deploy log	https://app.netlify.com/sites/cert-manager-website/deploys/6537d30b85283d0008a5cb42
😎 Deploy Preview	https://deploy-preview-1332--cert-manager-website.netlify.app
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[jetstack-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: wallrj

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