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
indexMetadataBuilder.version(indexMetadataBuilder.version() + 1);
            dedupeMapping(indexMetadataBuilder);
            IndexMetadata indexMetadata = indexMetadataBuilder.build();
            IndexMetadata previous = indices.put(indexMetadata.getIndex().getName(), indexMetadata);
            updateAliases(previous, indexMetadata);
            if (unsetPreviousIndicesLookup(previous, indexMetadata)) {
                previousIndicesLookup = null;
            }
            maybeSetMappingPurgeFlag(previous, indexMetadata);
            return this;
        }
        public Builder put(IndexMetadata indexMetadata, boolean incrementVersion) {
            final String name = indexMetadata.getIndex().getName();
            indexMetadata = dedupeMapping(indexMetadata);
            IndexMetadata previous;
            if (incrementVersion) {
                if (indices.get(name) == indexMetadata) {
                    return this;
                }
                
                indexMetadata = indexMetadata.withIncrementedVersion();
                previous = indices.put(name, indexMetadata);
            } else {
                previous = indices.put(name, indexMetadata);
                if (previous == indexMetadata) {
                    return this;
                }
            }
            updateAliases(previous, indexMetadata);
            if (unsetPreviousIndicesLookup(previous, indexMetadata)) {