Added time_in_execution attribute to /_cluster/pending_tasks response

[gargmanik13]

Description

Added time_in_execution attribute to /_cluster/pending_tasks response

• For task under execution we will get execution time in response
• For all other tasks, this will be zero

 OpenSearch git:(time_execution_metrics) ✗ curl -X GET "localhost:9200/_cluster/pending_tasks?pretty" \
     -H 'Content-Type: application/json'
{
  "tasks" : [
    {
      "insert_order" : 5,
      "priority" : "URGENT",
      "source" : "create-index [my_new_index], cause [api]",
      "executing" : true,
      "time_in_queue_millis" : 19703,
      "time_in_queue" : "19.7s",
      "time_in_execution_millis" : 19701,
      "time_in_execution" : "19.7s"
    },
    {
      "insert_order" : 6,
      "priority" : "URGENT",
      "source" : "create-index [my_new_index_2], cause [api]",
      "executing" : false,
      "time_in_queue_millis" : 8999,
      "time_in_queue" : "8.9s",
      "time_in_execution_millis" : 0,
      "time_in_execution" : "0s"
    },
    {
      "insert_order" : 7,
      "priority" : "URGENT",
      "source" : "create-index [my_new_index_3], cause [api]",
      "executing" : false,
      "time_in_queue_millis" : 3123,
      "time_in_queue" : "3.1s",
      "time_in_execution_millis" : 0,
      "time_in_execution" : "0s"
    }
  ]
}

Related Issues

Resolves #11818

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 991fe5f: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?