MUI PR 30241

• @2021-12-16
• Summary: enable search by https://mui.com/search?q=keyword
• See the PR
• The issue I made [docs] Implement search engine in v5 documentation page #29445
• This solves the issue #29945 raised by myself.
• Total time: ~4h.
  • Familiarize the repo ~1.5h
  • Learn JS Typing (painful) ~0.5h+
  • Learn Next JS dynamic routing ~0.5h
  • Documentation ~1h
• MUI has a large yet very neat repo.