loader should log where it found config files

In several places in Loader, such as here: https://github.com/apache/logging-log4j2/blob/2.x/log4j-core/src/main/java/org/apache/logging/log4j/core/util/Loader.java#L94 There’s a message at trace level saying basically “Trying to find [FILENAME] using THINGY”. This is very useful, because it lets you know all the places that log4j is looking for config files. However, there’s no good way to find which of these attempts succeeded. Earlier today I had to put a debug breakpoint inside this class to find out which log4j2.xml was getting loaded. It would be nice if successful attempts were logged, perhaps even at a level higher than trace. (maybe debug??)