Draft: Merge Workspace group projects and subgroups categories together

Why is this change being made?

This MR merges the categories ~"Category:Subgroups" and ~"Category:Projects" into a single category, Subgroups and Projects. This is intended to help support the consolidation of categories across Manage as part of this issue.

As part of the namespace consolidation project, projects and groups are consolidated into one namespace object, and a lot of the ongoing work concerns both subgroups and projects. It makes sense to describe further development efforts in one place and on one direction page. Projects in particular did not have a direction of its own so far.

If we decide to rename projects and groups into something else (this has yet to be determined), it would then also be a simpler change if those two are already consolidated.

Approval section

As per the handbook process:

• @david - VP of Product
• @ogolowinski - The Director of Product relevant to the affected Section(s)
• @timzallmann - The Director of Engineering relevant to the affected Section(s)
• @badnewsblair

The following people need to be on the merge request so they stay informed:

• @edjdev - Chief Technology Officer
• @clefelhocz1 VP of Development
• @tpazitny - Director of Quality Engineering
• @gl-quality/eng-prod Engineering Productivity (by @ mentioning @gl-quality/eng-prod)
• @cblake - The Product Marketing Manager relevant to the stage group(s)
• @susantacker - Senior Manager, Technical Writing

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.
• 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
• 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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