Support `npm` in `create-bolt-uxp`

In the spirit of supporting various frameworks it would be nice when yarn is opt-in. To support npm we have to check if the yarn command is available and propose to use npm otherwise. There are hints that yarn can be used alongside npm. Is this correct? I'm not able to implement this right now, but happy to do so when I can.

The affected lines in create-bolt-uxp:

bolt-uxp/create-bolt-uxp/src/build.ts

Line 246 in d9497ca

await execAsync(`cd ${fullPath} && yarn`);

bolt-uxp/create-bolt-uxp/src/build.ts

Line 272 in d9497ca

`cd ${path.basename(fullPath)} && yarn )`

@justintaylor-dev This is the key I mentioned yesterday: packageManager

It's part of an experimental feature called Corepack which needs to be enabled, but there are discussions going on to enable it by default.

Found this as well: which-pm-runs

Supports npm, pnpm, Yarn, cnpm, bun and any other package managers that set the npm_config_user_agent env variable.