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
if (allDataStreams.containsKey(dataStreamAlias)) {
                    aliasDuplicatesWithDataStreams.add(dataStreamAlias);
                }
            }
            for (String alias : indexAliases) {
                if (allDataStreams.containsKey(alias)) {
                    aliasDuplicatesWithDataStreams.add(alias);
                }
                if (indicesMap.containsKey(alias)) {
                    aliasDuplicatesWithIndices.add(alias);
                }
            }
            allDataStreams.forEach((key, value) -> {
                if (indicesMap.containsKey(key)) {
                    duplicates.add("data stream [" + key + "] conflicts with index");
                }
            });
            if (aliasDuplicatesWithIndices.isEmpty() == false) {
                collectAliasDuplicates(indicesMap, aliasDuplicatesWithIndices, duplicates);
            }
            if (aliasDuplicatesWithDataStreams.isEmpty() == false) {
                collectAliasDuplicates(indicesMap, dataStreamMetadata, aliasDuplicatesWithDataStreams, duplicates);
            }
            if (duplicates.isEmpty() == false) {
                throw new IllegalStateException(
                    "index, alias, and data stream names need to be unique, but the following duplicates "
                        + "were found ["
                        + Strings.collectionToCommaDelimitedString(duplicates)
                        + "]"
                );