fix: use normalized form for new configuration property

Author: ppkarwasz

log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternFormatter.java

@@ -40,7 +40,7 @@
 public interface InstantPatternFormatter extends InstantFormatter {
 
     boolean LEGACY_FORMATTERS_ENABLED =
-            "legacy".equalsIgnoreCase(PropertiesUtil.getProperties().getStringProperty("log4j2.instant.formatter"));
+            "legacy".equalsIgnoreCase(PropertiesUtil.getProperties().getStringProperty("log4j2.instantFormatter"));
 
     String getPattern();
 

src/site/antora/modules/ROOT/partials/manual/systemproperties/properties-log4j-core-misc.adoc

@@ -262,8 +262,8 @@ link:../javadoc/log4j-api/org/apache/logging/log4j/message/FlowMessageFactory.ht
 implementation to be used by all loggers.
 // end::flow-tracing[]
 
-[id=log4j2.instant.formatter]
-== `log4j2.instant.formatter`
+[id=log4j2.instantFormatter]
+== `log4j2.instantFormatter`
 
 [cols="1h,5"]
 |===