ESQL: Add documents_found and values_loaded (#125631)

[nik9000]

This adds documents_found and values_loaded to the to the ESQL response:

{
  "took" : 194,
  "is_partial" : false,
  "documents_found" : 100000,
  "values_loaded" : 200000,
  "columns" : [
    { "name" : "a", "type" : "long" },
    { "name" : "b", "type" : "long" }
  ],
  "values" : [[10, 1]]
}

These are cheap enough to collect that we can do it for every query and return it with every response. It's small, but it still gives you a reasonable sense of how much work Elasticsearch had to go through to perform the query.

I've also added these two fields to the driver profile and task status:

    "drivers" : [
      {
        "description" : "data",
        "cluster_name" : "runTask",
        "node_name" : "runTask-0",
        "start_millis" : 1742923173077,
        "stop_millis" : 1742923173087,
        "took_nanos" : 9557014,
        "cpu_nanos" : 9091340,
        "documents_found" : 5,   <---- THESE
        "values_loaded" : 15,    <---- THESE
        "iterations" : 6,
...

These are at a high level and should be easy to reason about. We'd like to extract this into a "show me how difficult this running query is" API one day. But today, just plumbing it into the debugging output is good.

Any Operator can claim to "find documents" or "load values" by overriding a method on its Operator.Status implementation:

/**
 * The number of documents found by this operator. Most operators
 * don't find documents and will return {@code 0} here.
 */
default long documentsFound() {
    return 0;
}

/**
 * The number of values loaded by this operator. Most operators
 * don't load values and will return {@code 0} here.
 */
default long valuesLoaded() {
    return 0;
}

In this PR all of the LuceneOperators declare that each position they emit is a "document found" and the ValuesSourceValuesSourceReaderOperator says each value it makes is a "value loaded". That's pretty pretty much true. The LuceneCountOperator and LuceneMinMaxOperator sort of pretend that the count/min/max that they emit is a "document" - but that's good enough to give you a sense of what's going on. It's like document.

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[nik9000]

Backport of #125631 to 8.19 long after the fact. Needed by #128828. Needs a change to main with the new transport version. That's incoming.

[nik9000]

Also needs a manual review from me to make sure the backport is truly just what it should be. It wasn't clean at all and I had to make a lot of modifications. I have to double check those are sane.

[nik9000]

Seems right to me modulo the three things I found. I'll fix those in a moment.

[nik9000]

This looks wrong. And it's wrong in main too!

[nik9000]

Leftover.

[nik9000]

Also in main. nuking.

[nik9000]

@idegtiarenko, could you have a look at this and double check it against the original PR? It looks right to me, but I'd appreciate a second set of eyes. And you are the one who needs this backport in so you get to suffer a little.