### Description

Currently async_search get or status response include the following info about async_search:

```
  "is_partial" : true, 
  "is_running" : true, 
  "start_time_in_millis" : 1583945890986,
  "expiration_time_in_millis" : 1584377890986,
```

In Kibana we would also like to have something like `completion_time` that would indicate time when the search was completed. It doesn't have to be precise, having some margin of error would be fine. 

**Some context:**

Currently Kibana uses background tasks to monitor completion of searches and it saves the completion time and then later shows it to users when they restore the search. Now we are simplifying the implementation of searches restoration on Kibana side and removing search monitoring in background tasks [(RFC here)](https://docs.google.com/document/d/1xpvW0xHmdm6w6EyYzYd01JLhiPFWF1Ij-tcJxCRLO7U/edit#) so Kibana can't longer track on its side the completion time. 

server/src/main/java/org/elasticsearch/TransportVersion.java
* Detached transport versions added below here.
     */
    public static final TransportVersion V_8_500_010 = registerTransportVersion(8_500_010, "9818C628-1EEC-439B-B943-468F61460675");
    public static final TransportVersion V_8_500_011 = registerTransportVersion(8_500_011, "2209F28D-B52E-4BC4-9889-E780F291C32E");
    public static final TransportVersion V_8_500_012 = registerTransportVersion(8_500_012, "BB6F4AF1-A860-4FD4-A138-8150FFBE0ABD");
    public static final TransportVersion V_8_500_013 = registerTransportVersion(8_500_013, "f65b85ac-db5e-4558-a487-a1dde4f6a33a");
    public static final TransportVersion V_8_500_014 = registerTransportVersion(8_500_014, "D115A2E1-1739-4A02-AB7B-64F6EA157EFB");
    public static final TransportVersion V_8_500_015 = registerTransportVersion(8_500_015, "651216c9-d54f-4189-9fe1-48d82d276863");
    public static final TransportVersion V_8_500_016 = registerTransportVersion(8_500_016, "492C94FB-AAEA-4C9E-8375-BDB67A398584");
    public static final TransportVersion V_8_500_017 = registerTransportVersion(8_500_017, "0EDCB5BA-049C-443C-8AB1-5FA58FB996FB");
    public static final TransportVersion V_8_500_018 = registerTransportVersion(8_500_018, "827C32CE-33D9-4AC3-A773-8FB768F59EAF");
    public static final TransportVersion V_8_500_019 = registerTransportVersion(8_500_019, "09bae57f-cab8-423c-aab3-c9778509ffe3");
    
    public static final TransportVersion V_8_500_020 = registerTransportVersion(8_500_020, "ECB42C26-B258-42E5-A835-E31AF84A76DE");
    public static final TransportVersion V_8_500_021 = registerTransportVersion(8_500_021, "102e0d84-0c08-402c-a696-935f3a3da873");
    
    public static final TransportVersion V_8_500_022 = registerTransportVersion(8_500_022, "4993c724-7a81-4955-84e7-403484610091");
    public static final TransportVersion V_8_500_023 = registerTransportVersion(8_500_023, "01b06435-5d73-42ff-a121-3b36b771375e");
    public static final TransportVersion V_8_500_024 = registerTransportVersion(8_500_024, "db337007-f823-4dbd-968e-375383814c17");
    public static final TransportVersion V_8_500_025 = registerTransportVersion(8_500_025, "b2ab7b75-5ac2-4a3b-bbb6-8789ca66722d");
    public static final TransportVersion V_8_500_026 = registerTransportVersion(8_500_026, "965d294b-14aa-4abb-bcfc-34631187941d");
    public static final TransportVersion V_8_500_027 = registerTransportVersion(8_500_027, "B151D967-8E7C-401C-8275-0ABC06335F2D");
    public static final TransportVersion V_8_500_028 = registerTransportVersion(8_500_028, "a6592d08-15cb-4e1a-b9b4-b2ba24058444");
    public static final TransportVersion V_8_500_029 = registerTransportVersion(8_500_029, "f3bd98af-6187-e161-e315-718a2fecc2db");
    public static final TransportVersion V_8_500_030 = registerTransportVersion(8_500_030, "b72d7f12-8ed3-4a5b-8e6a-4910ea10e0d7");
    public static final TransportVersion V_8_500_031 = registerTransportVersion(8_500_031, "e7aa7e95-37e7-46a3-aad1-90a21c0769e7");
    public static final TransportVersion V_8_500_032 = registerTransportVersion(8_500_032, "a9a14bc6-c3f2-41d9-a3d8-c686bf2c901d");
    public static final TransportVersion V_8_500_033 = registerTransportVersion(8_500_033, "193ab7c4-a751-4cbd-a66a-2d7d56ccbc10");
    public static final TransportVersion V_8_500_034 = registerTransportVersion(8_500_034, "16871c8b-88ba-4432-980a-10fd9ecad2dc");
    private static class CurrentHolder {