As discussed in #1837, we may want to make deleted workspaces fetchable instead of giving an error so that the user can see a workspace enter the deleted state.

This will probably need to be broken down into backend and frontend tickets, but I'll delay that until the plan is finalized.

• Make a request for a deleted workspace return the workspace (backend)
• Get rid of deleted workspaces after a certain amount of time (backend)
• Stay on the workspace page upon deletion (frontend)
• Add the ability to filter out deleted workspaces on the workspaces page (frontend)