Update dependencies to modern versions and address tech debt

In doing some preliminary checks into our packages for new versions and to resolve 2 high severity vulnerabilities, I found that many of our packages could be updated. In doing that, a lot of changes started to pile up, which would have created a nightmare to rebase and resolve once the 2 active patches get merged in.

This issue is to formalise the technical debt incurred over time in this project related to our packages and how we can update them to be more modern and less complicated.

• Update packages to latest where possible and address any vulnerabilities remaining in packages
• Remove @gitbeaker/node as it's unused
• Remove chai + chai-as-expected and replace with jest assertions
• Address the optional chaining code smell in project