No dependency caching when npm ci is used.

[joshwlewis]

Describe the bug

This buildpack currently prefers to install modules with npm ci over npm install. As stated in the npm docs, npm ci completely ignores any existing node_modules folder contents. It prefers instead to install from the global npm cache. However, this buildpack still attempts to persist and restore node_modules from the buildcache. This means we're using cycles, bandwidth and time caching and restoring artifacts that are completely ignored. Additionally, most builds aren't able to take advantage of any npm artifact caching, making them slower on subsequent builds.

To Reproduce
Build any Node.js app that uses npm to install dependencies.

Versions (please complete the following information):

• Heroku Stack: [heroku-18, heroku-20, heroku-22]
• Node Version: all
• NPM or Yarn Version: npm 6+
• Buildpack Version: heroku/nodejs v170 - heroku/nodejs v196

Additional context

Caching node_modules with npm install still works as intended. For folks wishing to speed up builds with caching, set the environment variable USE_NPM_INSTALL to true.