Display "time spent" in the tuple write/delete commands

[aaguiarz]

When a tuple write takes a long time, it's good to know how much it actually took.

We are currently adding these fields to the tuple write/delete commandas

{
  "failed_count": 1,
  "successful_count": 1,
  "total_count": 2
}```

We can also add `time spent`:

{
"failed_count": 1,
"successful_count": 1,
"total_count": 2
"time_spent": "10m 1s"
}```

It should be in "XXm YYs" format.

[Siddhant-K-code]

👋🏻 @aaguiarz, i've raised #450 to introduce this.