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
{
            int numEntries = randomIntBetween(4, 8);
            randomMappingDefinitions = Sets.newHashSetWithExpectedSize(numEntries);
            for (int i = 0; i < numEntries; i++) {
                Map<String, Object> mapping = RandomAliasActionsGenerator.randomMap(2);
                String mappingAsString = Strings.toString((builder, params) -> builder.mapContents(mapping));
                randomMappingDefinitions.add(mappingAsString);
            }
        }
        Metadata metadata;
        int numIndices = randomIntBetween(16, 32);
        {
            String[] definitions = randomMappingDefinitions.toArray(String[]::new);
            Metadata.Builder mb = new Metadata.Builder();
            for (int i = 0; i < numIndices; i++) {
                IndexMetadata.Builder indexBuilder = IndexMetadata.builder("index-" + i)
                    .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, IndexVersion.current()))
                    .putMapping(definitions[i % randomMappingDefinitions.size()])
                    .numberOfShards(1)
                    .numberOfReplicas(0);
                if (randomBoolean()) {
                    mb.put(indexBuilder);
                } else {
                    mb.put(indexBuilder.build(), true);
                }
            }
            metadata = mb.build();
        }
        assertThat(metadata.getMappingsByHash(), aMapWithSize(randomMappingDefinitions.size()));
        assertThat(