### Description

Given we have registered remotes and are able to cross cluster search/replicate I would like to be able to reindex a remote index on the local cluster.

The normal index from remote requires a host to be set. The proxy endpoint used for the remote doesn't work as that's over transport and index from remote uses the http/REST interface. Using the ES rest requires a user to be created with the correct permission, effectively not using the registered remote.

Doing a local index results in index not found:

```
# normal search works
POST remote1:example-index/_search

# results in index not found
POST _reindex
{
  "source": {
    "index": "remote1:example-index"
  },
  "dest": {
    "index": "my-new-example-index"
  }
}
```

```
{
  "error" : {
    "root_cause" : [
      {
        "type" : "index_not_found_exception",
        "reason" : "no such index [remote1:example-index]",
        "resource.type" : "index_or_alias",
        "resource.id" : "remote1:example-index",
        "index_uuid" : "_na_",
        "index" : "remote1:example-index"
      }
    ],
    "type" : "index_not_found_exception",
    "reason" : "no such index [remote1:example-index]",
    "resource.type" : "index_or_alias",
    "resource.id" : "remote1:example-index",
    "index_uuid" : "_na_",
    "index" : "remote1:example-index"
  },
  "status" : 404
}
```

modules/reindex/src/main/java/org/elasticsearch/reindex/ReindexValidator.java
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */
package org.elasticsearch.reindex;
import org.apache.lucene.util.automaton.Automata;
import org.apache.lucene.util.automaton.Automaton;
import org.apache.lucene.util.automaton.CharacterRunAutomaton;
import org.apache.lucene.util.automaton.MinimizationOperations;
import org.apache.lucene.util.automaton.Operations;
import org.elasticsearch.action.ActionRequestValidationException;
import org.elasticsearch.action.DocWriteRequest;
import org.elasticsearch.action.index.IndexRequest;
import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.support.AutoCreateIndex;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;