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.
modules/data-streams/src/javaRestTest/java/org/elasticsearch/datastreams/TsdbDataStreamRestIT.java
}
                            }
                        }
                    }
                }
            },
            "data_stream": {}
        }""";
    private static final String DOC = """
        {
            "@timestamp": "$time",
            "metricset": "pod",
            "k8s": {
                "pod": {
                    "name": "dog",
                    "uid":"df3145b3-0563-4d3b-a0f7-897eb2876ea9",
                    "ip": "10.10.55.3",
                    "network": {
                        "tx": 1434595272,
                        "rx": 530605511
                    }
                }
            }
        }
        """;
    private static final String BULK =
        """
            {"create": {}}
            {"@timestamp": "$now", "metricset": "pod", "k8s": {"pod": {"name": "cat", "uid":"947e4ced-1786-4e53-9e0c-5c447e959507", "ip": "10.10.55.1", "network": {"tx": 2001818691, "rx": 802133794}}}}
            {"create": {}}