Adding the subgroups/subdepartment under Quality in the overview for clarity purposes and easy access

Why is this change being made?

Going to each of the different sections under quality was not very easy. The structure is outlined over at handbook/engineering/quality/#quality-department-structure but it's not always clear how to navigate there. This makes it easier for others to find the respective part of the company that they're looking for.

I stayed away from the term 'sub-department' on purpose as only QE is a sub-department. The others (CS, QE, EP) are teams. Alternatively we can also just add QE as sub-department, similarly how Development is organized. The only disadvantage is that it doesn't solve the reason why I opened it in the first place.

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
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added, and the content is SAFE
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • 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.

---