feat: add ESM-specific rules

[ehmicky]

Part of https://github.com/netlify/team-dev/issues/36

Most of our repositories have migrated to pure ES modules. However, a few are still using CommonJS.
To accommodate with both and transition incrementally, this PR adds a new .eslintrc that contains rules specific to repositories which have migrated to pure ES modules.

Those will need to opt-in to it by switching from require('@netlify/eslint-config-node') to require('@netlify/eslint-config-node/esm'). After switching, they will also be able to clean up a few rules in their .eslintrc.

Checklist

Please add a x inside each checkbox:

• I have read the contribution guidelines.
• The status checks are successful (continuous integration). Those can be seen below.

[lukasholzer]

neat!