### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

all

### Problem Description

When you configure an `aggregate_metric_double` with `ignore_malformed: true` and send a malformed value we create an `_ignored` field with three values, `field.value_count`, `field.min`, and `field.max`. This is the only top "composite" field that creates `_ignored` values for its children. Things like shape only create `field` in `_ignored`. Is there a good reason for `aggregate_metric_double` to be different?

### Steps to Reproduce

see above

### Logs (if relevant)

_No response_
x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateDoubleMetricFieldMapperTests.java
public void testImplicitDefaultMetricSingleMetric() throws Exception {
        DocumentMapper mapper = createDocumentMapper(
            fieldMapping(b -> b.field("type", CONTENT_TYPE).field(METRICS_FIELD, new String[] { "value_count" }))
        );
        Mapper fieldMapper = mapper.mappers().getMapper("field");
        assertThat(fieldMapper, instanceOf(AggregateDoubleMetricFieldMapper.class));
        assertEquals(Metric.value_count, ((AggregateDoubleMetricFieldMapper) fieldMapper).defaultMetric);
    }
    /**
     * Test the default_metric when not set explicitly, by default we have set it to be the max.
     */
    public void testImplicitDefaultMetric() throws Exception {
        DocumentMapper mapper = createDocumentMapper(fieldMapping(this::minimalMapping));
        Mapper fieldMapper = mapper.mappers().getMapper("field");
        assertThat(fieldMapper, instanceOf(AggregateDoubleMetricFieldMapper.class));
        assertEquals(Metric.max, ((AggregateDoubleMetricFieldMapper) fieldMapper).defaultMetric);
    }
    /**
     * Test the default_metric when not set explicitly. When more than one metrics are contained
     * and max is not one of them, an exception should be thrown.
     */
    public void testMissingDefaultMetric() {
        Exception e = expectThrows(
            MapperParsingException.class,
            () -> createDocumentMapper(
                fieldMapping(b -> b.field("type", CONTENT_TYPE).field(METRICS_FIELD, new String[] { "value_count", "sum" }))
            )
        );
        assertThat(e.getMessage(), containsString("Property [default_metric] is required for field [field]."));
    }