feat: add sharing info to /workspaces endpoint (#21049)

closes: https://github.com/coder/internal/issues/858

Similar to https://github.com/coder/coder/pull/19375, this one uses
system permissions for fetching actual user and group data.

Modifies the `workspaces_expanded` view to fetch the required data; this way it's made available to all code paths that make use of it.  

Also fixes a bug in a test helper function that can result in `null` being saved to the DB for `user_acl` or `group_acl` and break tests; a defensive check constraint that prevents this is worth a PR, e.g:

`ALTER TABLE workspaces
   ADD CONSTRAINT group_acl_is_object CHECK (jsonb_typeof(group_acl) = 'object');`

Also adds missing  `OwnerName` in `ConvertWorkspaceRows`.

coderd/database/dbgen/dbgen.go

@@ -440,10 +440,18 @@ func Workspace(t testing.TB, db database.Store, orig database.WorkspaceTable) da
 		workspace.DormantAt = orig.DormantAt
 	}
 	if len(orig.UserACL) > 0 || len(orig.GroupACL) > 0 {
+		userACL := orig.UserACL
+		if userACL == nil {
+			userACL = database.WorkspaceACL{}
+		}
+		groupACL := orig.GroupACL
+		if groupACL == nil {
+			groupACL = database.WorkspaceACL{}
+		}
 		err = db.UpdateWorkspaceACLByID(genCtx, database.UpdateWorkspaceACLByIDParams{
 			ID:       workspace.ID,
-			UserACL:  orig.UserACL,
-			GroupACL: orig.GroupACL,
+			UserACL:  userACL,
+			GroupACL: groupACL,
 		})
 		require.NoError(t, err, "set workspace ACL")
 		workspace.UserACL = orig.UserACL