feat: add user display name field (#898)

Co-authored-by: Elias Schneider <login@eliasschneider.com>

backend/internal/utils/ptr_util.go

@@ -3,3 +3,11 @@ package utils
 func Ptr[T any](v T) *T {
 	return &v
 }
+
+func PtrValueOrZero[T any](ptr *T) T {
+	if ptr == nil {
+		var zero T
+		return zero
+	}
+	return *ptr
+}