Show number of workspaces per user or group in the GUI

[stirby]

In the /users and /groups pages, we could show the total number of workspaces that user/group has created (any state other than deleted). This allows admins to quickly determine which users/groups are creating the most workspaces.

And likewise for the groups page.

Note:
This would be empowered with a sorting option on both pages.

[stirby]

I'm somewhat hesitant to do this because we want this page to focus on user administration, not auditing. But it was requested by an enterprise customer.