Clang-format: add ordering rules for two more Flesnest headers

.clang-format

@@ -82,6 +82,10 @@ IncludeCategories:
     Priority:        1
   - Regex:           '^("|<).*slice'
     Priority:        2
+  - Regex:           '^("|<)Monitor.hpp'
+    Priority:        2
+  - Regex:           '^("|<)System.hpp'
+    Priority:        2
   - Regex:           '^("|<)Fair'
     Priority:        3
   - Regex:           '^("|<)Logger.h'