Migrate from v2 to v3

[filiptammergard]

This is what needs to be done when upgrading @einride/eslint-plugin from version 2 to version 3:

• prettier is removed as a direct dependency from the plugin and added as a peer dependency instead. If prettier is not already a dependency in your project, it should be added:

# npm
npm install prettier --save-dev

# yarn
yarn add prettier --dev

• eslint-plugin-prettier is upgraded to new major version which needs eslint to be version 7.28.0 or higher (this is also specified in peerDependencies). Make sure your project's eslint version is updated according to this!

# npm
npm install eslint@latest

# yarn
yarn upgrade eslint --latest