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
putCustom(IndexGraveyard.TYPE, indexGraveyard);
            return this;
        }
        public IndexGraveyard indexGraveyard() {
            return (IndexGraveyard) getCustom(IndexGraveyard.TYPE);
        }
        public Builder updateSettings(Settings settings, String... indices) {
            if (indices == null || indices.length == 0) {
                indices = this.indices.keys().toArray(new String[0]);
            }
            for (String index : indices) {
                IndexMetadata indexMetadata = this.indices.get(index);
                if (indexMetadata == null) {
                    throw new IndexNotFoundException(index);
                }
                // Updating vers
                // Otherwise, se
                long newVersion = indexMetadata.getSettingsVersion() + 1;
                put(
                    IndexMetadata.builder(indexMetadata)
                        .settings(Settings.builder().put(indexMetadata.getSettings()).put(settings))
                        .settingsVersion(newVersion)
                );
            }
            return this;
        }
        /**
         * Update the number of replicas for the specified indices.
         *
         * @param numberOfReplicas the number of replicas