Pnpm: Making installation faster on CI servers

[zkochan]

Installations on CI servers require less checks. With some assumptions, pnpm can work faster. Some ideas from Kat's cipm can be reused.

• [ ] unverified installation on CI servers #802

[rifler]

is this issue about npm ci command analogue in pnpm?

[ExE-Boss]

npm clean‑install is equivalent to pnpm install ‑‑frozen‑lockfile.

[zkochan]

Unlike npm, pnpm will automatically run a more efficient installation algorithm when the lockfile is up-to-date.

This issue is about making this installation even faster on CI environments as we can make some assumptions in such environment.