### Description

I was just looking at some Elasticsearch that had lots of "Improve "reloading search analyzers" logs coming from `MapperService` at the INFO level. In my particular case, it was being emitted because analyzers are reloaded as part of doing a recovery. This log is not really helpful as-is, I think we need to do the following:
 - Switch the level to DEBUG, it's not important enough to warrant an INFO log.
 - Add which index reloaded its search analyzers to the log.

What do you think?
server/src/main/java/org/elasticsearch/index/mapper/MapperService.java
String type2 = (String) mappings2.get("type");
            if (type2 == null && mappings2.get("properties") != null) {
                type2 = ObjectMapper.CONTENT_TYPE;
            }
            if (type1 == null || type2 == null) {
                return false;
            }
            return MERGEABLE_OBJECT_TYPES.contains(type1) && MERGEABLE_OBJECT_TYPES.contains(type2);
        }
    }
    public DocumentMapper merge(String type, CompressedXContent mappingSource, MergeReason reason) {
        final DocumentMapper currentMapper = this.mapper;
        if (currentMapper != null && currentMapper.mappingSource().equals(mappingSource)) {
            return currentMapper;
        }
        Map<String, Object> mappingSourceAsMap = MappingParser.convertToMap(mappingSource);
        return doMerge(type, reason, mappingSourceAsMap);
    }
    private synchronized DocumentMapper doMerge(String type, MergeReason reason, Map<String, Object> mappingSourceAsMap) {
        Mapping incomingMapping = parseMapping(type, mappingSourceAsMap);
        Mapping mapping = mergeMappings(this.mapper, incomingMapping, reason);
        
        
        DocumentMapper newMapper = newDocumentMapper(mapping, reason, mapping.toCompressedXContent());
        if (reason == MergeReason.MAPPING_UPDATE_PREFLIGHT) {
            return newMapper;
        }
        this.mapper = newMapper;
        assert assertSerialization(newMapper);
        return newMapper;