Add stats parameter to count API (#67528)

[kwnna15]

Adds stats parameter to the count API for the count API. Similar to what already exists in the search API:

(Optional, string) Specific tag of the request for logging and statistical purposes.

Example request:

curl -X GET "http://localhost:9200/my_index/_count" -H 'Content-Type: application/json' -d'
{
  "query": {
    "match_all": {}
  },
  "stats": ["stat_1"]
}'

Closes #67528

[elasticsearchmachine]

Pinging @elastic/es-search-foundations (Team:Search Foundations)

[javanna]

Sorry, this seems to have fallen through the cracks. #132963 is under review which fixes the same issue, hence I am closing this one.