[code-infra] Propagate pnpm engine in package.json

[oliviertassinari]

Summary

Based on the discussion https://github.com/mui/mui-toolpad/pull/3396#discussion_r1564881410, we have an opportunity to improve the reliability of dependency installs for contributors across all projects.

• preinstall script "npx only-allow pnpm"
• packageManager field
• engines.pnpm field

repositories

• [x] toolpad
• [x] X
• [x] base
• [x] pigment https://github.com/mui/pigment-css/pull/126
• [x] core
• [x] mui-private https://github.com/mui/mui-public/pull/169
• [ ] mui-public
• [ ] ?