Merge catalog groups with the same name/id into one group

[reginapramesti]

What this PR does

Fixes #4938

Implement v7 feature that allows having multiple catalog groups with the same name but different members, to allow having different catalog json files with the same top level group name

Checklist

• There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• I've updated CHANGES.md with what I changed.

[tephenavies]

Good to merge @KeyboardSounds or @nf-s when tests pass (tests pass locally).