Update naming from workspace to namespace

What does this MR do and why?

This MR updates naming from workspace to namespace in work items code

Groups and projects are namespaces, not workspaces, so we should update the naming to reflect this. The name workspace was used in the frontend before it became common for the backend to use namespaces, so the name workspace has just stuck around until now.

More workspace naming will be updated in subsequent MRs

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