Update fallback setting (elastic#118237) (elastic#118321)

Update synthetic_source_fallback_to_stored_source setting to be an operator only setting.

Author: martijnvg

x-pack/plugin/logsdb/src/main/java/org/elasticsearch/xpack/logsdb/SyntheticSourceLicenseService.java

@@ -38,7 +38,7 @@ final class SyntheticSourceLicenseService {
         "xpack.mapping.synthetic_source_fallback_to_stored_source",
         false,
         Setting.Property.NodeScope,
-        Setting.Property.Dynamic
+        Setting.Property.OperatorDynamic
     );
 
     static final LicensedFeature.Momentary SYNTHETIC_SOURCE_FEATURE = LicensedFeature.momentary(