Make camelcase and optional chaining play nicely

What does this MR do?

Make camelcase eslint rule work correctly for objects using optional chaining.

Previously we had to do this:

// eslint-disable-next-line camelcase
someObject?.with_camel_keys

Use updated babel-eslint-config https://gitlab.com/gitlab-org/gitlab-eslint-config/merge_requests/20

Remove disabled lint rule