Do not merge passthrough time series dimension mappers

Author: gmarouli

server/src/main/java/org/elasticsearch/index/mapper/ObjectMapper.java

@@ -227,7 +227,7 @@ protected final Map<String, Mapper> buildMappers(MapperBuilderContext mapperBuil
             for (Mapper.Builder builder : mappersBuilders) {
                 Mapper mapper = builder.build(mapperBuilderContext);
                 Mapper existing = mappers.get(mapper.leafName());
-                if (existing != null) {
+                if (existing != null && isPassThroughTimeSeriesDimension(mapper) == false) {
                     // The same mappings or document may hold the same field twice, either because duplicated JSON keys are allowed or
                     // the same field is provided using the object notation as well as the dot notation at the same time.
                     // This can also happen due to multiple index templates being merged into a single mappings definition using
@@ -245,6 +245,16 @@ protected final Map<String, Mapper> buildMappers(MapperBuilderContext mapperBuil
             return mappers;
         }
 
+        /**
+         * Pass through dimensions might be used in the index.routing_path so they should not be merged with existing field mappings
+         */
+        private boolean isPassThroughTimeSeriesDimension(Mapper mapper) {
+            if (mapper instanceof PassThroughObjectMapper passThroughObjectMapper) {
+                return passThroughObjectMapper.containsDimensions();
+            }
+            return false;
+        }
+
         @Override
         public ObjectMapper build(MapperBuilderContext context) {
             return new ObjectMapper(