Improves load.properties detection (#130)

* improve load.properties detection

* #130 If System.getProperty("load.properties") is specified that takes precedence

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Co-authored-by: Rob Bygrave <robin.bygrave@gmail.com>

Author: SentryMan

avaje-config/src/main/java/io/avaje/config/InitialLoadContext.java

@@ -137,6 +137,10 @@ CoreMap entryMap() {
    * Read the special properties that can point to an external properties source.
    */
   String indirectLocation() {
+    String location = System.getProperty("load.properties");
+    if (location != null) {
+      return location;
+    }
     var indirectLocation = map.get("load.properties");
     if (indirectLocation == null) {
       indirectLocation = map.get("load.properties.override");