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/main/java/org/elasticsearch/cluster/metadata/Metadata.java
DiffableUtils.getStringKeySerializer(),
                    CUSTOM_VALUE_SERIALIZER
                );
                reservedStateMetadata = DiffableUtils.diff(
                    before.reservedStateMetadata,
                    after.reservedStateMetadata,
                    DiffableUtils.getStringKeySerializer()
                );
            }
        }
        private static final DiffableUtils.DiffableValueReader<String, IndexMetadata> INDEX_METADATA_DIFF_VALUE_READER =
            new DiffableUtils.DiffableValueReader<>(IndexMetadata::readFrom, IndexMetadata::readDiffFrom);
        private static final DiffableUtils.DiffableValueReader<String, IndexTemplateMetadata> TEMPLATES_DIFF_VALUE_READER =
            new DiffableUtils.DiffableValueReader<>(IndexTemplateMetadata::readFrom, IndexTemplateMetadata::readDiffFrom);
        private static final DiffableUtils.DiffableValueReader<String, ReservedStateMetadata> RESERVED_DIFF_VALUE_READER =
            new DiffableUtils.DiffableValueReader<>(ReservedStateMetadata::readFrom, ReservedStateMetadata::readDiffFrom);
        private MetadataDiff(StreamInput in) throws IOException {
            empty = false;
            clusterUUID = in.readString();
            clusterUUIDCommitted = in.readBoolean();
            version = in.readLong();
            coordinationMetadata = new CoordinationMetadata(in);
            transientSettings = Settings.readSettingsFromStream(in);
            persistentSettings = Settings.readSettingsFromStream(in);
            if (in.getTransportVersion().onOrAfter(TransportVersion.V_7_3_0)) {
                hashesOfConsistentSettings = DiffableStringMap.readDiffFrom(in);
            } else {
                hashesOfConsistentSettings = DiffableStringMap.DiffableStringMapDiff.EMPTY;
            }
            indices = DiffableUtils.readImmutableOpenMapDiff(in, DiffableUtils.getStringKeySerializer(), INDEX_METADATA_DIFF_VALUE_READER);