**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/test/java/org/elasticsearch/xpack/transform/transforms/TransformFailureHandlerTests.java
static class MockTransformContextListener implements TransformContext.Listener {
        private boolean failed = false;
        private int failureCountChangedCounter = 0;
        public void reset() {
            failed = false;
            failureCountChangedCounter = 0;
        }
        @Override
        public void shutdown() {
        }
        @Override
        public void failureCountChanged() {
            failureCountChangedCounter++;
        }
        @Override
        public void fail(String failureMessage, ActionListener<Void> listener) {
            failed = true;
        }
        public boolean getFailed() {
            return failed;
        }
        public int getFailureCountChangedCounter() {
            return failureCountChangedCounter;
        }
    }
    public void testUnattended() {
        String transformId = randomAlphaOfLength(10);