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
originalThread
                    );
                    i++;
                }
            }
        });
    }
    private void executePipelines(
        final int slot,
        final Iterator<String> it,
        final boolean hasFinalPipeline,
        final IndexRequest indexRequest,
        final IntConsumer onDropped,
        final BiConsumer<Integer, Exception> onFailure,
        final AtomicInteger counter,
        final BiConsumer<Thread, Exception> onCompletion,
        final Thread originalThread
    ) {
        assert it.hasNext();
        final String pipelineId = it.next();
        try {
            PipelineHolder holder = pipelines.get(pipelineId);
            if (holder == null) {
                throw new IllegalArgumentException("pipeline with id [" + pipelineId + "] does not exist");
            }
            Pipeline pipeline = holder.pipeline;
            String originalIndex = indexRequest.indices()[0];
            innerExecute(slot, indexRequest, pipeline, onDropped, e -> {
                if (e != null) {
                    logger.debug(