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
mappingsByHash,
            oldestIndexVersion,
            reservedStateMetadata
        );
    }
    /**
     * Creates a copy of this instance updated with the given {@link IndexMetadata} that must only contain changes to primary terms
     * and in-sync allocation ids relative to the existing entries. This method is only used by
     * {@link org.elasticsearch.cluster.routing.allocation.IndexMetadataUpdater#applyChanges(Metadata, RoutingTable)}.
     * @param updates map of index name to {@link IndexMetadata}.
     * @return updated metadata instance
     */
    public Metadata withAllocationAndTermUpdatesOnly(Map<String, IndexMetadata> updates) {
        if (updates.isEmpty()) {
            return this;
        }
        final var updatedIndicesBuilder = ImmutableOpenMap.builder(indices);
        updatedIndicesBuilder.putAllFromMap(updates);
        return new Metadata(
            clusterUUID,
            clusterUUIDCommitted,
            version,
            coordinationMetadata,
            transientSettings,
            persistentSettings,
            settings,
            hashesOfConsistentSettings,
            totalNumberOfShards,
            totalOpenIndexShards,
            updatedIndicesBuilder.build(),