**Affected version:** 7.12 - 7.17.7, 8.0-8.5
**Fixed in:** 7.17.7, 8.5.0

### Problem Description

A continuous transform can fail if a transform is searching at the same time as an ILM action occurs or in general anything that closes an index. This should not happen if transform is configured with a wildcard pattern for the source index, e.g. `filebeat-*`.

In a specific case an ILM policy temporarily closes the index due to the unfollow-the-follower action.

A typical log entry for this bugs contains something like this:

```
task encountered irrecoverable failure: org.elasticsearch.cluster.block.ClusterBlockException: index [ ... ] blocked by: [FORBIDDEN/4/index closed];
```

### Mitigation

A: Restart the transform. This can be automated by monitoring `_stats` and restarting the transform using `_stop?force=true` followed by `_start`.

B: Don't use the ILM unfollow action until a fix is available.

C: **Unreleased**: Starting with 8.5 set the transform to `unattended` mode via `settings`, this will let transform retry even for this failure class

### Solution

If the source of a transform is configured with a wildcard, transform should not treat an index closed exception as an irrecoverable failure.

### Backport

The fix needs to be backported to the `7.17` series.
x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/TransformFailureHandler.java
1 - (Math.log10(pageSize) * 0.1)
        );
        int newPageSize = (int) Math.round(reducingFactor * pageSize);
        if (newPageSize < TransformIndexer.MINIMUM_PAGE_SIZE) {
            String message = TransformMessages.getMessage(TransformMessages.LOG_TRANSFORM_PIVOT_LOW_PAGE_SIZE_FAILURE, pageSize);
            if (unattended) {
                retry(circuitBreakingException, message, true, -1);
            } else {
                fail(message);
            }
        } else {
            String message = TransformMessages.getMessage(TransformMessages.LOG_TRANSFORM_PIVOT_REDUCE_PAGE_SIZE, pageSize, newPageSize);
            auditor.info(transformId, message);
            logger.info("[{}] {}", transformId, message);
            context.setPageSize(newPageSize);
        }
    }
    /**
     * Handle script exception case. This is error is irrecoverable.
     *
     * @param scriptException ScriptException thrown
     * @param unattended whether the transform runs in unattended mode
     */
    private void handleScriptException(ScriptException scriptException, boolean unattended) {
        String message = TransformMessages.getMessage(
            TransformMessages.LOG_TRANSFORM_PIVOT_SCRIPT_ERROR,
            scriptException.getDetailedMessage(),
            scriptException.getScriptStack()
        );
        if (unattended) {