Package-level JS config files

[ecraig12345]

This is just a tracking issue, not necessarily something there's a plan to implement unless there's a compelling need.

Originally, beachball intended to allow JS config files per-package. This was broken in #405 which appears to be unintentional. (It also may not have been working quite as expected to begin with because the logic prior to that PR would have searched up and returned the repo config if there was no package config.) Even though removal of this feature was unintentional, it's been gone for a long time now (meaning nobody is relying on it), and restoring the behavior of searching for a bunch of config files when reading each package would slow down perf.

If we need package-level JS configs in the future, a better approach would be to support a package.json beachball property which is a string pointing to the config file: e.g. "beachball": "beachball.config.js". Then use cosmiconfig 's load(packageJson.beachball) to load the file.