Add async_method_call to utility

Adding async_method_call in dbus utility gives us a place where we can
intercept method call requests from dbus to potentially add
logging/caching.

An example of logging is in the later commit:
https://gerrit.openbmc.org/c/openbmc/bmcweb/+/78265/

We already do this for setProperty, this moves the method calls to
follow a similar pattern.

Tested: Redfish service validator passes.

Change-Id: I6d2c96e2b6b6a023ed2138106a55faebca161592
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/redfish-core/lib/led.hpp b/redfish-core/lib/led.hpp
index e868bf3..b74dc4d 100644
--- a/redfish-core/lib/led.hpp
+++ b/redfish-core/lib/led.hpp
@@ -20,6 +20,7 @@
 #include <array>
 #include <functional>
 #include <memory>
+#include <string>
 #include <string_view>
 #include <utility>