Add ProbeLab page to Concepts

[ElPaisano]

Address https://github.com/ipfs/ipfs-docs/issues/1698

Tasks

• [x] Create 'measurements.md' page in Concepts to talk about ProbeLab
  • [x] Discuss KPIs
  • [x] Discuss tooling
• [ ] GH actions
  • [ ] Links
  • [ ] Spelling
  • [x] Formatting