[BUG] DataStreams: Can't delete index template that matches the data stream but is unused

[Jakob3xD]

Describe the bug
It is not possible to delete an index template matching a data stream that is not used by the data stream.

To Reproduce
Steps to reproduce the behavior:
1.

PUT _index_template/test
{
  "index_patterns": [
    "test*"
  ],
  "template": {},
  "composed_of": [],
  "priority": 50
}

PUT _index_template/test-data-stream
{
  "index_patterns": [
    "test"
  ],
  "data_stream": {},
  "template": {},
  "composed_of": [],
  "priority": 51
}

3. PUT _data_stream/test
4. DELETE _index_template/test
5. Get following error:

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "unable to remove composable templates [test] as they are in use by a data streams [test]"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "unable to remove composable templates [test] as they are in use by a data streams [test]"
  },
  "status": 400
}

Expected behavior
It should be possible to delete the index template as it is not used.

Plugins

opensearch-alerting
opensearch-anomaly-detection
opensearch-asynchronous-search
opensearch-cross-cluster-replication
opensearch-geospatial
opensearch-index-management
opensearch-job-scheduler
opensearch-knn
opensearch-ml
opensearch-neural-search
opensearch-notifications
opensearch-notifications-core
opensearch-observability
opensearch-reports-scheduler
opensearch-security
opensearch-security-analytics
opensearch-sql
prometheus-exporter
repository-s3

Host/Environment (please complete the following information):

• Setup: Docker on Ubuntu
• Opensearch: v2.8.0

Additional information:
elastic/elasticsearch#84376

[Jakob3xD]

Current workaround to delete the template is to set the index_patterns to something else that does not match the data_stream. So for my example it would be:

PUT _index_template/test
{
  "index_patterns": [
    "foo"
  ],
  "template": {},
  "composed_of": [],
  "priority": 50
}

DELETE _index_template/test