[Feature Request] Pipeline ingest processor supports ignoring the non-existing pipeline

[gaobinlong]

Is your feature request related to a problem? Please describe

Now the pipeline ingest processor always throws exception Pipeline processor configured for non-existent pipeline [non-existen] if the specified pipeline doesn't exist:

POST _ingest/pipeline/_simulate
{
  "pipeline": {
    "processors": [
      {
        "pipeline": {
          "name" : "non-existen"
        }
      }
    ]
  },
  "docs": [
    {
      "_source": {
        "foo": "bar"
      }
    }
  ]
}

Describe the solution you'd like

The pipeline ingest processor supports a parameter like ignore_missing, when the specified pipeline doesn't exist and the parameter is set to true, the processor exit quietly.

Related component

Indexing

Describe alternatives you've considered

No alternatives.

Additional context

No response

[peternied]

[Triage - attendees 1 2 3 4 5]
@gaobinlong Thanks for creating this issue; however, it isn't being accepted due to this making the outcome of this request non-deterministic. Please feel free to open a new issue after addressing the reason.

@msfroh Do you have additional thoughts?