Implement RFC 0014: Enable support for Yarn Berry #118
Description
Context
In an effort to enable building Yarn Berry applications, the API of the yarn-install buildpack has been modified to accomodate those applications which do not utillize node_modules.
Details
The buildpack's detection logic should be modified to require yarn_pkgs in addition to node_modules, thereby enabling running build scripts for Yarn Berry applications.
Acceptance Criteria
Given an app which uses Yarn Berry and has build scripts defined in package.json:
- The buildpack should pass detection
- The buildpack should successfully run the specified build scripts.