We use `totalMetrics` with a `startTimeInNanos` and a call to `postIngest` to track the 'total time' that ingest is running for a given document. You can imagine it's a little stopwatch that we start and stop. Unfortunately, I think we're stopping the stopwatch just a little too soon, on the start side, we include the time spent transforming the document into an `IngestDocument`, but we do not include the (non-negligible) time transforming from an `IngestDocument` after the pipeline logic has run.

That is, the call to `sourceAsMap` is included:

https://github.com/elastic/elasticsearch/blob/d03664f84f15dcfcb900cf2d43121ca9d89bdda8/server/src/main/java/org/elasticsearch/ingest/IngestService.java#L905

But the call to `source` is not:

https://github.com/elastic/elasticsearch/blob/d03664f84f15dcfcb900cf2d43121ca9d89bdda8/server/src/main/java/org/elasticsearch/ingest/IngestService.java#L948

The consequence of this is that the `total` ingest stats doesn't actually reflect the true time spent in ingest code:

```
GET _nodes/stats?filter_path=nodes.*.ingest
{
  "nodes" : {
    "Aysm6ztIRne2ES5ktyuqtw" : {
      "ingest" : {
        "total" : {
          "count" : 1,
          "time_in_millis" : 110, <--- this should be a little higher than it is
```
server/src/main/java/org/elasticsearch/ingest/IngestService.java
}
                if (newIt.hasNext()) {
                    executePipelines(
                        slot,
                        newIt,
                        newHasFinalPipeline,
                        indexRequest,
                        onDropped,
                        onFailure,
                        counter,
                        onCompletion,
                        originalThread
                    );
                } else {
                    if (counter.decrementAndGet() == 0) {
                        onCompletion.accept(originalThread, null);
                    }
                    assert counter.get() >= 0;
                }
            });
        } catch (Exception e) {
            logger.debug(
                () -> format("failed to execute pipeline [%s] for document [%s/%s]", pipelineId, indexRequest.index(), indexRequest.id()),
                e
            );
            onFailure.accept(slot, e);
            if (counter.decrementAndGet() == 0) {
                onCompletion.accept(originalThread, null);
            }
            assert counter.get() >= 0;