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

[jpmat296]

Describe the bug

This issue is similar to #9194. But in #9194 the two index templates were not data streams templates (no "data_stream": {} for the first).

In this new issue, the two index templates are both for data streams.

Related component

Indexing

To Reproduce

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

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

PUT _data_stream/test

DELETE _index_template/test

Get following error at DELETE time:

{
  "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.

Additional Details

Setup: Docker on macOS
Opensearch: v3.3.2

[gaobinlong]

This is really a bug, very similar to #9194, taking look into this.