[docs] Revise Example Projects and Related Projects pages

[samuelsycamore]

part of #40062

To clarify the purpose of each of these pages so there's no confusion or overlap - move "Community Projects" from Example Projects to Related Projects and reorganize the lists accordingly.

Also removed several outdated community projects - those which have not been updated to v5+.

Preview:

• https://deploy-preview-44191--material-ui.netlify.app/material-ui/discover-more/related-projects/
• https://deploy-preview-44191--material-ui.netlify.app/material-ui/getting-started/example-projects/

Example projects

• list official (i.e. maintained by MUI) third-party integrations - minimal scaffolds and boilerplates
• link to (official) free and paid templates
• community developers should not be encouraged to open PRs to link their projects here

Related projects

• list community-led projects and tools that incorporate or extend Material UI
• community developers can open PRs to link to their projects here

Showcase (beyond the scope of this PR)

• live projects, products, and apps that use Material UI

[mui-bot]

Netlify deploy preview

• docs/data/material/discover-more/related-projects/related-projects.md
• docs/data/material/getting-started/example-projects/example-projects.md

Bundle size report

No bundle size changes (Toolpad)
No bundle size changes

Generated by 🚫 dangerJS against e837c80

[samuelsycamore]

Maybe the h4s are unnecessary on the Related projects page? They're kind of redundant since there's only one item listed under each. We could remove them and just list all of the supplementary components under the h3.

[aarongarciah]

✨

[oliviertassinari]

Rich text -> Rich text editor

I was about to make this same change 👍. I got confused reading Rich text on this page today.