Add flat_map to includes

A recent change made it so that flat_map is not transitively included by
object_server.hpp in sdbusplus.  Explicitly add the required enum.

Tested: Code builds.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I50ee58bf194400358b8af29b653f22d4aabd8daa
diff --git a/include/me_to_redfish_hooks.hpp b/include/me_to_redfish_hooks.hpp
index d8250c0..1f80a1a 100644
--- a/include/me_to_redfish_hooks.hpp
+++ b/include/me_to_redfish_hooks.hpp
@@ -15,6 +15,7 @@
 */
 
 #pragma once
+#include <boost/container/flat_map.hpp>
 #include <ipmi_to_redfish_hooks.hpp>
 
 namespace intel_oem::ipmi::sel::redfish_hooks::me
@@ -182,4 +183,4 @@
     }
 }
 } // namespace utils
-} // namespace intel_oem::ipmi::sel::redfish_hooks::me
\ No newline at end of file
+} // namespace intel_oem::ipmi::sel::redfish_hooks::me