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/test/java/org/elasticsearch/cluster/metadata/MetadataTests.java
builder.put(idx, true);
            DataStream dataStream = newInstance(dataStreamName, List.of(idx.getIndex()));
            builder.put(dataStream);
            Metadata metadata = builder.build();
            assertThat(previous.getIndicesLookup(), not(sameInstance(metadata.getIndicesLookup())));
            previous = metadata;
        }
        {
            Metadata.Builder builder = Metadata.builder(previous);
            builder.put(dataStreamAliasName, dataStreamName, false, null);
            Metadata metadata = builder.build();
            assertThat(previous.getIndicesLookup(), not(sameInstance(metadata.getIndicesLookup())));
            previous = metadata;
        }
        {
            Metadata.Builder builder = Metadata.builder(previous);
            builder.put(dataStreamAliasName, dataStreamName, true, null);
            Metadata metadata = builder.build();
            assertThat(previous.getIndicesLookup(), not(sameInstance(metadata.getIndicesLookup())));
            previous = metadata;
        }
        {
            Metadata.Builder builder = Metadata.builder(previous);
            builder.put(
                IndexMetadata.builder(indexName)
                    .settings(settings(IndexVersion.current()))
                    .creationDate(randomNonNegativeLong())
                    .numberOfShards(1)
                    .numberOfReplicas(0)
            );