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
"@timestamp" : {
                            "type": "date"
                        },
                        "metricset": {
                            "type": "keyword"
                        },
                        "k8s": {
                            "properties": {
                                "pod": {
                                    "properties": {
                                        "uid": {
                                            "type": "keyword"
                                        },
                                        "name": {
                                            "type": "keyword"
                                        },
                                        "ip": {
                                            "type": "ip"
                                        },
                                        "network": {
                                            "properties": {
                                                "tx": {
                                                    "type": "long"
                                                },
                                                "rx": {
                                                    "type": "long"
                                                }
                                            }
                                        }
                                    }