Support for alternative package manager

[lachrist]

At the moment, the agent is only tested against npm it might be worthwhile to support alternative package managers such as yarn and pnpm.

    ["npx", name],
    ["npx.cmd", name],
    ["npm", "exec", name],
    ["npm.cmd", "exec", name],

You might also consider supporting yarn [{exec,dlx}] and whatever the equivalent for pnpm is.
@dividedmind

[lachrist]

Duplicate of #168