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 = Metadata.builder(metadata);
        String newAliasName = "alias-new";
        {
            builder.put(
                IndexMetadata.builder(newAliasName + "-1")
                    .settings(settings(IndexVersion.current()))
                    .creationDate(randomNonNegativeLong())
                    .numberOfShards(1)
                    .numberOfReplicas(0)
                    .putAlias(new AliasMetadata.Builder(newAliasName).writeIndex(true))
            );
        }
        metadata = builder.build();
        assertThat(metadata.aliasedIndices(), hasSize(numAliases + 1));
        assertThat(metadata.aliasedIndices(newAliasName), contains(new Index(newAliasName + "-1", ClusterState.UNKNOWN_UUID)));
        
        builder = Metadata.builder(metadata);
        {
            builder.remove(newAliasName + "-1");
        }
        metadata = builder.build();
        assertThat(metadata.aliasedIndices(), hasSize(numAliases));
        assertThat(metadata.aliasedIndices(newAliasName), empty());
        
        builder = Metadata.builder(metadata);
        {
            IndexMetadata.Builder imBuilder = new IndexMetadata.Builder(metadata.index("alias-1-0"));
            imBuilder.putAlias(new AliasMetadata.Builder(newAliasName));
            builder.put(imBuilder);
            imBuilder = new IndexMetadata.Builder(metadata.index("alias-2-1"));