IndicatorLED: Add a deprecated warning header

Added a warning header when IndicatorLED is patched telling the
client it is deprecated and pointing to LocationIndicatorActive.

Used the warning syntax from
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Warning

Tested: curl -X PATCH -v -d '{ "IndicatorLED":"Off"}'  \
        -k https://$bmc/redfish/v1/Systems/system
       ...
< HTTP/1.1 204 No Content
< Warning: 299 - "IndicatorLED is deprecated. Use LocationIndicatorActive instead."
< Strict-Transport-Security: max-age=31536000; includeSubdomains; preload
< X-Frame-Options: DENY

Change-Id: Ic25a02508b0a1bcada1fa71ffa413c493fad00c4
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/redfish-core/lib/systems.hpp b/redfish-core/lib/systems.hpp
index 2817d92..9325a93 100644
--- a/redfish-core/lib/systems.hpp
+++ b/redfish-core/lib/systems.hpp
@@ -2233,6 +2233,9 @@
         if (indicatorLed)
         {
             setIndicatorLedState(asyncResp, *indicatorLed);
+            res.addHeader(boost::beast::http::field::warning,
+                          "299 - \"IndicatorLED is deprecated. Use "
+                          "LocationIndicatorActive instead.\"");
         }
 
         if (powerRestorePolicy)