Add JS linter to the docs codebase

We are at a point where we're adding more and more JS to the docs codebase.

I suggest we add a JavaScript linter such as ESLint to help us standardize and improve the quality of our codebase.

Benefits

Code linting has many benefits, and we're already benefitting from linting yaml and scss in the docs codebase.

• Improves code quality.

• Align the docs codebase with the product codebase.

• Enforcing a styleguide can help engineers adhere to our styleguide rules which can help prevent illegible code.

• Less work for reviewers during code review.

• Reduces bug-prone code by identifying syntax errors.

• etc