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/test/java/org/elasticsearch/datastreams/DataStreamIndexSettingsProviderTests.java
}
            }
            """;
        Settings result = generateTsdbSettings(mapping, now);
        assertThat(result.size(), equalTo(3));
        assertThat(IndexSettings.TIME_SERIES_START_TIME.get(result), equalTo(now.minusMillis(lookAheadTime.getMillis())));
        assertThat(IndexSettings.TIME_SERIES_END_TIME.get(result), equalTo(now.plusMillis(lookAheadTime.getMillis())));
        assertThat(IndexMetadata.INDEX_ROUTING_PATH.get(result), containsInAnyOrder("host.id", "prometheus.labels.*"));
    }
    public void testGenerateRoutingPathFromDynamicTemplate_templateWithNoPathMatch() throws Exception {
        Instant now = Instant.now().truncatedTo(ChronoUnit.SECONDS);
        TimeValue lookAheadTime = TimeValue.timeValueHours(2); 
        String mapping = """
            {
                "_doc": {
                    "dynamic_templates": [
                        {
                            "labels": {
                                "path_match": "prometheus.labels.*",
                                "mapping": {
                                    "type": "keyword",
                                    "time_series_dimension": true
                                }
                            }
                        },
                        {
                            "strings_as_keyword": {
                                "match_mapping_type": "string",
                                "mapping": {
                                    "type": "keyword",