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
"type": "geo_point"
                    },
                    "area": {
                      "type": "geo_shape", \s
                      "tree": "quadtree",
                      "precision": "1m"
                    }
                  }
                },
                "properties": {
                  "type": "nested",
                  "properties": {
                    "key" : {
                      "type": "text",
                      "fields": {
                        "keyword" : {
                          "type" : "keyword"
                        }
                      }
                    },
                    "value" : {
                      "type": "text",
                      "fields": {
                        "keyword" : {
                          "type" : "keyword"
                        }
                      }
                    }
                  }
                }