docs(core): show 404 content instead of redirecting to intro

[jaysoo]

Shows a 404 message and keep URL intact, instead of redirecting to the intro page. This way we can track them better.

Example: https://nx-dev-git-fork-jaysoo-docs-show-404-nrwl.vercel.app/four-oh-four

Current Behavior

Expected Behavior

Related Issue(s)

Fixes #

[nx-cloud-staging]

☁️ Nx Cloud Report

CI is running/has finished running commands for commit 01ac28c. As they complete they will appear below. Click to see the status, the terminal output, and the build insights.

📂 See all runs for this branch

---

✅ Successfully ran 12 targets

• nx affected --target=e2e --base=c7249db3861d0ed1fa7d47b360825ee8f4d27b5f --head=01ac28ccc8dfc168389baad5cbb2af1c71c9d01a --exclude=e2e-storybook,e2e-storybook-angular,e2e-react-native,e2e-detox,e2e-make-angular-cli-faster --parallel=1
• nx-cloud record -- yarn depcheck
• nx affected --target=test --base=c7249db3861d0ed1fa7d47b360825ee8f4d27b5f --head=01ac28ccc8dfc168389baad5cbb2af1c71c9d01a --parallel=1
• nx-cloud record -- yarn nx workspace-lint
• nx-cloud record -- yarn check-lock-files
• nx affected --target=build --base=c7249db3861d0ed1fa7d47b360825ee8f4d27b5f --head=01ac28ccc8dfc168389baad5cbb2af1c71c9d01a --parallel=3
• nx affected --target=lint --base=c7249db3861d0ed1fa7d47b360825ee8f4d27b5f --head=01ac28ccc8dfc168389baad5cbb2af1c71c9d01a --parallel=3
• nx-cloud record -- yarn check-commit
• nx-cloud record -- yarn nx format:check --base=c7249db3861d0ed1fa7d47b360825ee8f4d27b5f --head=01ac28ccc8dfc168389baad5cbb2af1c71c9d01a
• nx-cloud record -- yarn check-imports
• nx-cloud record -- yarn documentation
• nx build typedoc-theme

---

Sent with 💌 from NxCloud.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated
nx-dev	✅ Ready (Inspect)	Visit Preview	Aug 30, 2022 at 5:51PM (UTC)

[github-actions]

This pull request has already been merged/closed. If you experience issues related to these changes, please open a new issue referencing this pull request.