
Filing this issue to track a question/comment that was raised by @ywangd  here https://github.com/elastic/elasticsearch/pull/98309#discussion_r1294115440

One question I do have is why we chose to [execute the LookupRequest with the enrich origin](https://github.com/elastic/elasticsearch/blob/2e4440ff1c0decf79f8a40688566411f7d518aa7/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/enrich/EnrichLookupService.java#L141C2-L141C2). It means the following query works when the user has access to only the playlist index without access to either the songs enrich policy or its associated index.

```
FROM playlist | ENRICH songs ON song_id
```

It feels a bit weird to me that we have no control on who can use what enrich process. That said, we don't have a good story around enrich and ingest pipeline either, i.e. we have no control over who can use what pipeline where a pipeline can contain an enrich processor. There have been quite a few complaints from users and we have an https://github.com/elastic/elasticsearch/issues/57586 for it. I wonder whether we should not repeat the problem here with ES|QL. On the surface, it might be easier to tackle compared to ingest pipelines since ES|QL is read-only and has no "bulk" operations. What do you think?
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizer.java
SplitInWithFoldableValue() {
            super(TransformDirection.UP);
        }
        @Override
        protected Expression rule(In in) {
            if (in.value().foldable()) {
                List<Expression> foldables = new ArrayList<>(in.list().size());
                List<Expression> nonFoldables = new ArrayList<>(in.list().size());
                in.list().forEach(e -> {
                    if (e.foldable() && Expressions.isNull(e) == false) { 
                        foldables.add(e);
                    } else {
                        nonFoldables.add(e);
                    }
                });
                if (foldables.size() > 0 && nonFoldables.size() > 0) {
                    In withFoldables = new In(in.source(), in.value(), foldables);
                    In withoutFoldables = new In(in.source(), in.value(), nonFoldables);
                    return new Or(in.source(), withFoldables, withoutFoldables);
                }
            }
            return in;
        }
    }
    private static class BooleanSimplification extends org.elasticsearch.xpack.ql.optimizer.OptimizerRules.BooleanSimplification {