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
assertThat(value.getType(), equalTo(IndexAbstraction.Type.DATA_STREAM));
        value = metadata.getIndicesLookup().get("d3");
        assertThat(value, notNullValue());
        assertThat(value.getType(), equalTo(IndexAbstraction.Type.DATA_STREAM));
        value = metadata.getIndicesLookup().get("d4");
        assertThat(value, notNullValue());
        assertThat(value.getType(), equalTo(IndexAbstraction.Type.DATA_STREAM));
        value = metadata.getIndicesLookup().get("a1");
        assertThat(value, notNullValue());
        assertThat(value.getType(), equalTo(IndexAbstraction.Type.ALIAS));
        value = metadata.getIndicesLookup().get("a2");
        assertThat(value, notNullValue());
        assertThat(value.getType(), equalTo(IndexAbstraction.Type.ALIAS));
        value = metadata.getIndicesLookup().get("a3");
        assertThat(value, notNullValue());
        assertThat(value.getType(), equalTo(IndexAbstraction.Type.ALIAS));
    }
    public void testDataStreamAliasValidation() {
        Metadata.Builder b = Metadata.builder();
        addDataStream("my-alias", b);
        b.put("my-alias", "my-alias", null, null);
        var e = expectThrows(IllegalStateException.class, b::build);
        assertThat(e.getMessage(), containsString("data stream alias and data stream have the same name (my-alias)"));
        b = Metadata.builder();
        addDataStream("d1", b);
        addDataStream("my-alias", b);
        b.put("my-alias", "d1", null, null);
        e = expectThrows(IllegalStateException.class, b::build);
        assertThat(e.getMessage(), containsString("data stream alias and data stream have the same name (my-alias)"));
        b = Metadata.builder();