Chore: Fix error handling in postDashboard, remove UserDisplayDTO, fix live redis client initialization (#87206)

* clean up error handling in postDashboard and remove UserDisplayDTO

* replace GetUserUID with GetUID and GetNamespacedUID, enforce namespace constant type

* lint fix

* lint fix

* more lint fixes

pkg/services/dashboardsnapshots/database/database.go

@@ -137,8 +137,8 @@ func (d *DashboardSnapshotStore) SearchDashboardSnapshots(ctx context.Context, q
 
 		namespace, id := query.SignedInUser.GetNamespacedID()
 		var userID int64
-		switch namespace {
-		case identity.NamespaceServiceAccount, identity.NamespaceUser:
+
+		if namespace == identity.NamespaceServiceAccount || namespace == identity.NamespaceUser {
 			var err error
 			userID, err = identity.IntIdentifier(namespace, id)
 			if err != nil {