[WebOS] Add a Header file for fixing build error (project-chip#36278)

Change
 - Added a header file in WebOS Platform to fix build error

Testing
 - Tested done on WebOS

Author: jungwook-park

src/platform/webos/DiagnosticDataProviderImpl.cpp

@@ -24,6 +24,7 @@
 #include <platform/internal/CHIPDeviceLayerInternal.h>
 
 #include <lib/support/CHIPMem.h>
+#include <lib/support/CHIPMemString.h>
 #include <lib/support/logging/CHIPLogging.h>
 #include <platform/DiagnosticDataProvider.h>
 #include <platform/webos/ConnectivityUtils.h>