Add include of forward header in forward.cpp jinja template.

aidge_core/export_utils/templates/forward.jinja

@@ -6,6 +6,8 @@
 #include <sys/stat.h>
 #endif
 
+#include "include/forward.hpp"
+
 // Layer & memory configurations
 {%- for header in headers %}
 #include "{{ header }}"