Enhance ES|QL responses to include information about `took` time (search latency), shards, and
clusters against which the query was executed.
The goal of this PR is to begin to provide parity between the metadata displayed for
cross-cluster searches in _search and ES|QL.
This PR adds the following features:
- add overall `took` time to all ES|QL query responses. And to emphasize: "all" here
means: async search, sync search, local-only and cross-cluster searches, so it goes
beyond just CCS.
- add `_clusters` metadata to the final response for cross-cluster searches, for both
async and sync search (see example below)
- tracking/reporting counts of skipped shards from the can_match (SearchShards API)
phase of ES|QL processing
- marking clusters as skipped if they cannot be connected to (during the field-caps
phase of processing)
Out of scope for this PR:
- honoring the `skip_unavailable` cluster setting
- showing `_clusters` metadata in the async response **while** the search is still running
- showing any shard failure messages (since any shard search failures in ES|QL are
automatically fatal and _cluster/details is not shown in 4xx/5xx error responses). Note that
this also means that the `failed` shard count is always 0 in ES|QL `_clusters` section.
Things changed with respect to behavior in `_search`:
- the `timed_out` field in `_clusters/details/mycluster` was removed in the ESQL
response, since ESQL does not support timeouts. It could be added back later
if/when ESQL supports timeouts.
- the `failures` array in `_clusters/details/mycluster/_shards` was removed in the ESQL
response, since any shard failure causes the whole query to fail.
Example output from ES|QL CCS:
```es
POST /_query
{
"query": "from blogs,remote2:bl*,remote1:blogs|\nkeep authors.first_name,publish_date|\n limit 5"
}
```
```json
{
"took": 49,
"columns": [
{
"name": "authors.first_name",
"type": "text"
},
{
"name": "publish_date",
"type": "date"
}
],
"values": [
[
"Tammy",
"2009-11-04T04:08:07.000Z"
],
[
"Theresa",
"2019-05-10T21:22:32.000Z"
],
[
"Jason",
"2021-11-23T00:57:30.000Z"
],
[
"Craig",
"2019-12-14T21:24:29.000Z"
],
[
"Alexandra",
"2013-02-15T18:13:24.000Z"
]
],
"_clusters": {
"total": 3,
"successful": 2,
"running": 0,
"skipped": 1,
"partial": 0,
"failed": 0,
"details": {
"(local)": {
"status": "successful",
"indices": "blogs",
"took": 43,
"_shards": {
"total": 13,
"successful": 13,
"skipped": 0,
"failed": 0
}
},
"remote2": {
"status": "skipped", // remote2 was offline when this query was run
"indices": "remote2:bl*",
"took": 0,
"_shards": {
"total": 0,
"successful": 0,
"skipped": 0,
"failed": 0
}
},
"remote1": {
"status": "successful",
"indices": "remote1:blogs",
"took": 47,
"_shards": {
"total": 13,
"successful": 13,
"skipped": 0,
"failed": 0
}
}
}
}
}
```
Fixes https://github.com/elastic/elasticsearch/issues/112402 and https://github.com/elastic/elasticsearch/issues/110935
ddba47407d