In https://github.com/elastic/elasticsearch/pull/78547 we introduced batching for the ILM master tasks that occur on the happy path. However if a high-shard-count cluster encounters problems while doing ILM-related things—perhaps some nodes are temporarily unavailable for taking a snapshot—then we process the resulting `ilm-retry-failed-step` and `ilm-move-to-error-step` tasks one-by-one which can significantly delay the cluster's recovery from its problems.

We should batch these things together too.

It looks like we also enqueue duplicate `ilm-retry-failed-step` on each poll interval too, although we do appear to treat the duplicates as no-ops at execution time.

Relates https://github.com/elastic/elasticsearch/issues/77466
x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/ilm/MoveToErrorStepUpdateTaskTests.java
long now = randomNonNegativeLong();
        Exception cause = new ElasticsearchException("THIS IS AN EXPECTED CAUSE");
        setStateToKey(notCurrentStepKey);
        MoveToErrorStepUpdateTask task = new MoveToErrorStepUpdateTask(
            index,
            policy,
            currentStepKey,
            cause,
            () -> now,
            (idxMeta, stepKey) -> new MockStep(stepKey, new StepKey("next-phase", "action", "step")),
            state -> {}
        );
        ClusterState newState = task.execute(clusterState);
        assertThat(newState, sameInstance(clusterState));
    }
    public void testExecuteNoopDifferentPolicy() throws IOException {
        StepKey currentStepKey = new StepKey("current-phase", "current-action", "current-name");
        long now = randomNonNegativeLong();
        Exception cause = new ElasticsearchException("THIS IS AN EXPECTED CAUSE");
        setStateToKey(currentStepKey);
        setStatePolicy("not-" + policy);
        MoveToErrorStepUpdateTask task = new MoveToErrorStepUpdateTask(
            index,
            policy,
            currentStepKey,
            cause,
            () -> now,
            (idxMeta, stepKey) -> new MockStep(stepKey, new StepKey("next-phase", "action", "step")),
            state -> {}
        );