**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
userIndicesClone.removeAll(checkpointsByIndex.keySet());
            if (userIndicesClone.isEmpty() == false) {
                logger.debug("Original set of user indices contained more indexes [{}]", userIndicesClone);
            }
        }
        
        Map<String, long[]> checkpointsByIndexReduced = new TreeMap<>();
        checkpointsByIndex.forEach(
            (indexName, checkpoints) -> {
                checkpointsByIndexReduced.put(indexName, checkpoints.values().stream().mapToLong(l -> l).toArray());
            }
        );
        return checkpointsByIndexReduced;
    }
    @Override
    public void getCheckpointingInfo(
        TransformCheckpoint lastCheckpoint,
        TransformCheckpoint nextCheckpoint,
        TransformIndexerPosition nextCheckpointPosition,
        TransformProgress nextCheckpointProgress,
        ActionListener<TransformCheckpointingInfoBuilder> listener
    ) {
        TransformCheckpointingInfo.TransformCheckpointingInfoBuilder checkpointingInfoBuilder =
            new TransformCheckpointingInfo.TransformCheckpointingInfoBuilder();
        checkpointingInfoBuilder.setLastCheckpoint(lastCheckpoint)
            .setNextCheckpoint(nextCheckpoint)
            .setNextCheckpointPosition(nextCheckpointPosition)
            .setNextCheckpointProgress(nextCheckpointProgress);
        long timestamp = clock.millis();
        getIndexCheckpoints(ActionListener.wrap(checkpointsByIndex -> {