Update gem and bundler in Gitpod before installing Ruby dependencies

What does this MR do and why?

I noticed when launching this project in Gitpod that the version of bundler available after !3487 (merged) is still pretty old.

This MR effectively adds gem update --system to the initialization calls, but does it by using the existing make targets.

Screenshots, screen recordings, or links to review app

Open this branch in Gitpod to see the effect of the changes.

Merge request acceptance checklist

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• I have evaluated the MR acceptance checklist for this merge request.