**Affected version:** 8.2 - 8.5.2
**Fixed in:** 8.5.3

### Problem Description

The problem applies to transforms that use more than 1 CCS cluster or 1 local and 1 CCS as source. A typical source could look like this (the important part: `remotes*`):

```
        "index" : [
          "remotes*:filebeat*"
        ],

```

If 2 indices share the same name the transform might fail with an error similar to this:

```
 Failed to retrieve checkpoint due to: Duplicate key logs-2022-11-14 (attempted merging values [... and ...]
```

Similar to the above the `_stats` call is broken for such a transform, it can fail with an error message starting with:

```
Failure during checkpoint retrieval
```

This can happen even if the transform is in state `STOPPED` or `FAILED`.

### Mitigation

Choose _one_ of the following mitigations:

 - split your transforms to use max 1 CCS/local indices

_or_

 - avoid upgrading to 8.2, until the issue got resolved (this is a regression of #80984)

_or_

 - avoid duplicate names for your indices even on remote cluster, e.g. name the index: `remote1-filebeat...`, `remote2-filebeat...`


### Solution

This is a regression of #80984 which introduced a new way of check-pointing. The remote needs to be prefixed to the index name.
x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/checkpoint/DefaultCheckpointProvider.java
int shardNo = i;
                                logger.warn(
                                    () -> Strings.format(
                                        "Source has [%s] failed shards, shard failure [%s]",
                                        response.getFailedShards(),
                                        shardNo
                                    ),
                                    response.getShardFailures()[i]
                                );
                            }
                            listener.onFailure(
                                new CheckpointException(
                                    "Source has [{}] failed shards, first shard failure: {}",
                                    response.getShardFailures()[0],
                                    response.getFailedShards(),
                                    response.getShardFailures()[0].toString()
                                )
                            );
                            return;
                        }
                        listener.onResponse(extractIndexCheckPoints(response.getShards(), userIndices, cluster));
                    }, e -> listener.onFailure(new CheckpointException("Failed to create checkpoint", e)))
                );
            }, e -> listener.onFailure(new CheckpointException("Failed to create checkpoint", e)))
        );
    }
    static Map<String, long[]> extractIndexCheckPoints(ShardStats[] shards, Set<String> userIndices, String cluster) {
        Map<String, TreeMap<Integer, Long>> checkpointsByIndex = new TreeMap<>();
        for (ShardStats shard : shards) {
            String indexName = shard.getShardRouting().getIndexName();