Currently it is possible to migrate an existing data stream to a time series data stream.
This is done by updating the index template that created the data stream. 
Then after a rollover the data stream is a time series data stream. 

Via a similar way it should be possible to change time series data stream back 
to a regular data stream. Currently when changing the `index.mode` setting
on an index template from `time_series` to `standard` (or removing the setting)
results in a validation error.
modules/data-streams/src/javaRestTest/java/org/elasticsearch/datastreams/TsdbDataStreamRestIT.java
"network": {
                                            "properties": {
                                                "tx": {
                                                    "type": "long"
                                                },
                                                "rx": {
                                                    "type": "long"
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            },
            "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,