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
public Builder remove(String index) {
            previousIndicesLookup = null;
            checkForUnusedMappings = true;
            IndexMetadata previous = indices.remove(index);
            updateAliases(previous, null);
            return this;
        }
        public Builder removeAllIndices() {
            previousIndicesLookup = null;
            checkForUnusedMappings = true;
            indices.clear();
            mappingsByHash.clear();
            aliasedIndices.clear();
            return this;
        }
        public Builder indices(Map<String, IndexMetadata> indices) {
            for (var value : indices.values()) {
                put(value, false);
            }
            return this;
        }
        void updateAliases(IndexMetadata previous, IndexMetadata current) {
            if (previous == null && current != null) {
                for (var key : current.getAliases().keySet()) {
                    putAlias(key, current.getIndex());
                }
            } else if (previous != null && current == null) {
                for (var key : previous.getAliases().keySet()) {
                    removeAlias(key, previous.getIndex());
                }