docs: create v4.md to document breaking changes

docs/breaking-changes/v4.md

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+# Upgrade from v3 to v4
+
+- `actions-node/lint`: This update changes the action's behavior from just running `eslint` to running an npm script passed by the consumer that would run all the lint checks they need.
+
+## Description of changes
+
+- `actions-node/lint`: The action now takes an input `lint-script`, which is the name of the npm script it is going to run as the primary lint check. The default value of the input is `lint`, meaning the action will run `yarn lint` or `npm run lint` depending on the package manager the consumer is using (which is picked up automatically).
+
+## Upgrade instructions
+
+- `actions-node/lint`: If the npm script to lint your code locally is anything other than `lint`, pass it to the `lint-script` input.