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
* Cluster state task executor for ingest pipeline operations
     */
    static final ClusterStateTaskExecutor<PipelineClusterStateUpdateTask> PIPELINE_TASK_EXECUTOR = batchExecutionContext -> {
        final var allIndexMetadata = batchExecutionContext.initialState().metadata().indices().values();
        final IngestMetadata initialIngestMetadata = batchExecutionContext.initialState().metadata().custom(IngestMetadata.TYPE);
        var currentIngestMetadata = initialIngestMetadata;
        for (final var taskContext : batchExecutionContext.taskContexts()) {
            try {
                final var task = taskContext.getTask();
                try (var ignored = taskContext.captureResponseHeaders()) {
                    currentIngestMetadata = task.execute(currentIngestMetadata, allIndexMetadata);
                }
                taskContext.success(() -> task.listener.onResponse(AcknowledgedResponse.TRUE));
            } catch (Exception e) {
                taskContext.onFailure(e);
            }
        }
        final var finalIngestMetadata = currentIngestMetadata;
        return finalIngestMetadata == initialIngestMetadata
            ? batchExecutionContext.initialState()
            : batchExecutionContext.initialState().copyAndUpdateMetadata(b -> b.putCustom(IngestMetadata.TYPE, finalIngestMetadata));
    };
    /**
     * Specialized cluster state update task specifically for ingest pipeline operations.
     * These operations all receive an AcknowledgedResponse.
     */
    public abstract static class PipelineClusterStateUpdateTask implements ClusterStateTaskListener {
        final ActionListener<AcknowledgedResponse> listener;
        PipelineClusterStateUpdateTask(ActionListener<AcknowledgedResponse> listener) {
            this.listener = listener;