CLI: Use pnpm to install packages if project is using pnpm

[IanVS]

Is your feature request related to a problem? Please describe
The problem occurs when adding storybook into a project that has been bootsrapped using pnpm. We already have logic to detect whether the project is using npm or yarn, but not pnpm. And when trying to yarn install or npm install, an error is thrown on pnpm vite projects:

npm ERR! code EUNSUPPORTEDPROTOCOL
npm ERR! Unsupported URL Type "workspace:": workspace:*

To reproduce, in a new folder, run:

pnpm create vite@latest . --template=react
pnpm i
pnpx sb@next init

Describe the solution you'd like
We should look for a pnpm-lock.json file in the project, and if found, use pnpm install.

Describe alternatives you've considered
N/A

Are you able to assist to bring the feature to reality?
Yes, I can give it a shot.

[shilman]

Ta-da!! I just released https://github.com/storybookjs/storybook/releases/tag/v7.0.0-alpha.39 containing PR #19425 that references this issue. Upgrade today to the @next NPM tag to try it out!

npx sb upgrade --prerelease

Closing this issue. Please re-open if you think there's still more to do.