### 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
+ "incoming:\n"
                + incomingMappingSource
                + "\nmerged:\n"
                + mergedMappingSource;
        return true;
    }
    boolean assertNoUpdateRequired(final IndexMetadata newIndexMetadata) {
        MappingMetadata mapping = newIndexMetadata.mapping();
        if (mapping != null) {
            
            
            
            
            
            Mapping newMapping = parseMapping(mapping.type(), mapping.source());
            final CompressedXContent currentSource = this.mapper.mappingSource();
            final CompressedXContent newSource = newMapping.toCompressedXContent();
            if (Objects.equals(currentSource, newSource) == false
                && mapper.isSyntheticSourceMalformed(currentSource, indexVersionCreated) == false) {
                throw new IllegalStateException(
                    "expected current mapping [" + currentSource + "] to be the same as new mapping [" + newSource + "]"
                );
            }
        }
        return true;
    }
    public void merge(IndexMetadata indexMetadata, MergeReason reason) {
        assert reason != MergeReason.MAPPING_UPDATE_PREFLIGHT;
        MappingMetadata mappingMetadata = indexMetadata.mapping();
        if (mappingMetadata != null) {