[ML] Remote clusters can't be excluded using "-" from AD datafeed

[wwang500]

Version: 8.15.1

Step to reproduce:

1. Setup two remote clusters: cluster1, cluster2
2. Load kibana sample data on both remote cluster1 and remote cluster2
3. Create a dataview to exclude one of them: ":kibana,-cluster1:*"
4. Create a simple AD job using the above dataview
5. at the last step of AD job wizard, it will hit a no_such_remote_cluster_exception error:

{
  "statusCode": 404,
  "error": "Not Found",
  "message": "[no_such_remote_cluster_exception\n\tRoot causes:\n\t\tno_such_remote_cluster_exception: no such remote cluster: [-cluster1]]: no such remote cluster: [-cluster1]",
  "attributes": {
    "body": {
      "error": {
        "root_cause": [
          {
            "type": "no_such_remote_cluster_exception",
            "reason": "no such remote cluster: [-cluster1]"
          }
        ],
        "type": "no_such_remote_cluster_exception",
        "reason": "no such remote cluster: [-cluster1]"
      },
      "status": 404
    }
  }
}

Workaround:

1. don't use "-" to exclude, instead, explicitly include remotes by names
2. use a query to exclude remote clusters:

   "bool": {
     "must_not": [
       {
         "terms": {
           "_index": [
             "cluster1:*"
           ]
         }
       }
     ]
   }

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)