A composable index template with no `template` defined in the body is mistakingly always assumed to not be a time series template. Even if it refers to a component template that has the `index.mode` setting set to `time_series` and the component template defines mappings with dimension fields or routing paths.

Incorrectly this causes to create a data stream with a tsdb index *without* time series start and end time settings set. The fact that this can happen is another bug and is being tracked #98833.

What should happen in this case is that a tsdb data stream is created with a valid tsdb backing index (with correctly generated time series start and end time settings).

This bug was found as part investigating #98792 and is the cause of that bug.
server/src/test/java/org/elasticsearch/cluster/metadata/MetadataTests.java
MappingMetadata updatedMapping = new MappingMetadata(MapperService.SINGLE_MAPPING_NAME, Map.of("mapping", "updated"));
        {
            Metadata.Builder mb = new Metadata.Builder(metadata);
            mb.put(IndexMetadata.builder(luckyIndex).putMapping(updatedMapping));
            metadata = mb.build();
        }
        assertThat(metadata.getMappingsByHash(), aMapWithSize(randomMappingDefinitions.size() + 1));
        assertThat(metadata.getMappingsByHash().get(luckyIndex.mapping().getSha256()), equalTo(entry));
        assertThat(metadata.getMappingsByHash().get(updatedMapping.getSha256()), equalTo(updatedMapping));
        
        {
            Metadata.Builder mb = new Metadata.Builder(metadata);
            mb.remove(luckyIndex.getIndex().getName());
            metadata = mb.build();
        }
        assertThat(metadata.getMappingsByHash(), aMapWithSize(randomMappingDefinitions.size()));
        assertThat(metadata.getMappingsByHash().get(updatedMapping.getSha256()), nullValue());
        
        MappingMetadata newMapping = new MappingMetadata(MapperService.SINGLE_MAPPING_NAME, Map.of("new", "mapping"));
        {
            Metadata.Builder mb = new Metadata.Builder(metadata);
            mb.put(
                IndexMetadata.builder("index-" + numIndices)
                    .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, IndexVersion.current()))
                    .putMapping(newMapping)
                    .numberOfShards(1)
                    .numberOfReplicas(0)
            );
            metadata = mb.build();
        }