Draft: Add an Internal tab to explore/groups

What does this MR do and why?

Describe in detail what your merge request does and why.

Adds an internal groups tab to the explore pages. Currently this shows any internally-visible groups but also those to which the user is a member.

Related #389041 (closed) and #395283

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

> Your groups

> Internal groups

> Explore public groups

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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