### 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
public static final TransportVersion V_7_7_0 = registerTransportVersion(7_07_00_99, "7bb73c48-ddb8-4437-b184-30371c35dd4b");
    public static final TransportVersion V_7_8_0 = registerTransportVersion(7_08_00_99, "c3cc74af-d15e-494b-a907-6ad6dd2f4660");
    public static final TransportVersion V_7_8_1 = registerTransportVersion(7_08_01_99, "7acb9f6e-32f2-45ce-b87d-ca1f165b8e7a");
    public static final TransportVersion V_7_9_0 = registerTransportVersion(7_09_00_99, "9388fe76-192a-4053-b51c-d2a7b8eae545");
    public static final TransportVersion V_7_10_0 = registerTransportVersion(7_10_00_99, "4efca195-38e4-4f74-b877-c26fb2a40733");
    public static final TransportVersion V_7_10_1 = registerTransportVersion(7_10_01_99, "0070260c-aa0b-4fc2-9c87-5cd5f23b005f");
    public static final TransportVersion V_7_11_0 = registerTransportVersion(7_11_00_99, "3b43bcbc-1c5e-4cc2-a3b4-8ac8b64239e8");
    public static final TransportVersion V_7_12_0 = registerTransportVersion(7_12_00_99, "3be9ff6f-2d9f-4fc2-ba91-394dd5ebcf33");
    public static final TransportVersion V_7_13_0 = registerTransportVersion(7_13_00_99, "e1fe494a-7c66-4571-8f8f-1d7e6d8df1b3");
    public static final TransportVersion V_7_14_0 = registerTransportVersion(7_14_00_99, "8cf0954c-b085-467f-b20b-3cb4b2e69e3e");
    public static final TransportVersion V_7_15_0 = registerTransportVersion(7_15_00_99, "2273ac0e-00bb-4024-9e2e-ab78981623c6");
    public static final TransportVersion V_7_15_1 = registerTransportVersion(7_15_01_99, "a8c3503d-3452-45cf-b385-e855e16547fe");
    public static final TransportVersion V_7_16_0 = registerTransportVersion(7_16_00_99, "59abadd2-25db-4547-a991-c92306a3934e");
    public static final TransportVersion V_7_17_0 = registerTransportVersion(7_17_00_99, "322efe93-4c73-4e15-9274-bb76836c8fa8");
    public static final TransportVersion V_7_17_1 = registerTransportVersion(7_17_01_99, "51c72842-7974-4669-ad25-bf13ba307307");
    public static final TransportVersion V_7_17_8 = registerTransportVersion(7_17_08_99, "82a3e70d-cf0e-4efb-ad16-6077ab9fe19f");
    public static final TransportVersion V_8_0_0 = registerTransportVersion(8_00_00_99, "c7d2372c-9f01-4a79-8b11-227d862dfe4f");
    public static final TransportVersion V_8_1_0 = registerTransportVersion(8_01_00_99, "3dc49dce-9cef-492a-ac8d-3cc79f6b4280");
    public static final TransportVersion V_8_2_0 = registerTransportVersion(8_02_00_99, "8ce6d555-202e-47db-ab7d-ade9dda1b7e8");
    public static final TransportVersion V_8_3_0 = registerTransportVersion(8_03_00_99, "559ddb66-d857-4208-bed5-a995ccf478ea");
    public static final TransportVersion V_8_4_0 = registerTransportVersion(8_04_00_99, "c0d12906-aa5b-45d4-94c7-cbcf4d9818ca");
    public static final TransportVersion V_8_5_0 = registerTransportVersion(8_05_00_99, "be3d7f23-7240-4904-9d7f-e25a0f766eca");
    public static final TransportVersion V_8_6_0 = registerTransportVersion(8_06_00_99, "e209c5ed-3488-4415-b561-33492ca3b789");
    public static final TransportVersion V_8_6_1 = registerTransportVersion(8_06_01_99, "9f113acb-1b21-4fda-bef9-2a3e669b5c7b");
    public static final TransportVersion V_8_7_0 = registerTransportVersion(8_07_00_99, "f1ee7a85-4fa6-43f5-8679-33e2b750448b");
    public static final TransportVersion V_8_7_1 = registerTransportVersion(8_07_01_99, "018de9d8-9e8b-4ac7-8f4b-3a6fbd0487fb");
    public static final TransportVersion V_8_8_0 = registerTransportVersion(8_08_00_99, "f64fe576-0767-4ec3-984e-3e30b33b6c46");
    public static final TransportVersion V_8_8_1 = registerTransportVersion(8_08_01_99, "291c71bb-5b0a-4b7e-a407-6e53bc128d0f");
    /*
     * READ THE JAVADOC ABOVE BEFORE ADDING NEW TRANSPORT VERSIONS