chore: auto-detect preferred package manager in Dockerfile

[balazsorban44]

Noticed while I had a look at #38686. We don't need to ask the user to comment in/out sections in the Dockerfile, as we can detect the package manager they prefer based on which lockfile we copied over.

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
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Documentation / Examples

• Make sure the linting passes by running pnpm lint
• The examples guidelines are followed from our contributing doc

[balazsorban44]

There is wget -qO- https://get.pnpm.io/install.sh | sh - also, but I got some errors while trying that locally, so I stuck with yarn global add pnpm. Is this a bad idea? 🤔

[SukkaW]

Why not npm i pnpm -g🤔?
https://pnpm.io/installation#using-npm

[balazsorban44]

yarn might be slightly faster, I think. haven't tested it though