### Description

We have had this longstanding issue that running a top-level `filter` aggregation is often (not always, e.g. not if you need the total hit count too) a performance bug, as Elasticsearch would iterate over docs that match the `query` and would then check each of these docs against the filter of the `filter` aggregation. It's usually a better idea to put the filter directly into the query, where it can be used to drive iteration if appropriate.

We could do this automatically by implementing the `LeafCollector#competitiveIterator` API that was introduced for dynamic pruning, in order to automatically start intersecting the query with the filter of the `filter` aggregator once enough hits have been counted.
server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregator.java
final DocCountProvider docCount;
        private long count;
        Counter(DocCountProvider docCount) {
            this.docCount = docCount;
        }
        public long readAndReset(LeafReaderContext ctx) throws IOException {
            long result = count;
            count = 0;
            docCount.setLeafReaderContext(ctx);
            return result;
        }
        @Override
        public void collect(int doc) throws IOException {
            count += docCount.getDocCount(doc);
        }
        @Override
        public void setScorer(Scorable scorer) throws IOException {}
    }
}