Add support for Yarn

[ezzatron]

Yarn is great. It would be nice to support it.

Interestingly, yarn install features a --pure-lockfile flag, which seems perfect for usage with composer-npm-bridge. It's a pity that NPM doesn't support something similar.

Relates to #20.

[ezzatron]

I just found out about npm ci, which looks awesome.

So the behavior could be something like this:

• Choose a "driver":
  • Can be manually specified in composer.json extra.npm-bridge.driver
  • Defaults to "yarn" if yarn.lock is present in the package root
  • Falls back to "npm"
• If using the Yarn driver:
  • If the lock file is present, install packages with yarn install --pure-lockfile
  • If the lock file is absent, install packages with yarn install --no-lockfile
• If using the NPM driver:
  • If the lock file is present, install packages with npm ci
  • If the lock file is absent, install packages with npm install --no-package-lock