[Feature Request]: Support `pnpm` package manager

[kindoflew]

Describe your request

We currently only support npm and yarn. pnpm is the new hotness, so we should support it as well.

Possible Implementation

The logic for which package manager commands to use lives in src/queries/getPackageManager.ts, so we would just need to add it as an option in the getPackageManager function and then add it's corresponding commands to the PACKAGE_MANAGER object in that file.

Also, many of the pnpm commands actually just fall through to using npm under the hood, so the implementation details should be very similar.

Code of Conduct

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