Create the CSS Utilities working group

Why is this change being made?

Creates the CSS Utilities working group.

Rendered page in the Review App: https://css-working-group.about.gitlab-review.app/company/team/structure/working-groups/css/

The general purpose of this working group is to address general challenges that the frontend department faces when it comes to CSS. Through tooling improvements and migrations, we'll focus on:

• Reducing CSS bundles size.
• Enforcing Pajamas-compliance.
• Improving developer experience (DX).

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
  • The when to get approval handbook section explains the workflow in more detail
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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