PD-ctl should show the timestamps in a consistent way

[coderplay]

When we call pd-ctl store , it shows the timestamps in 4 different ways, see below example:

    {
      "store": {
...
        "git_hash": "6c1424706f3d5885faa668233f34c9f178302f36",
        "start_timestamp": 1647365006,                                              <=========  10 digits unix timestamp
...
        "last_heartbeat": 1647373317633963588,                              <========= 19 digits unix timestamp
        "state_name": "Up"
      },
      "status": {
....
        "start_ts": "2022-03-15T17:23:26Z",                                        <========= YYYY-MM-DDTHH:mm:ss
        "last_heartbeat_ts": "2022-03-15T19:41:57.633963588Z",   <========= YYYY-MM-DDTHH:mm:ss:nnnnnnnnn
...
      }
    }

It's pretty hard to evaluate the difference between unix timestamps and the date time format. Please \ show the timestamps in a consistent way.

[rleungx]

Thanks for your feedback but considering the compatibility problems, we will try to make them consistent in API version 2.

[nolouch]

ref tikv/rfcs#88