Use float64 for network rate stats

[amogh09]

Summary

Changing the type of network rate stats RxBytesPerSecond and TxBytesPerSecond in ecs-agent module from float32 to float64 to match Fargate Agent.

The change in behavior for TMDS v4 is that network_rate_stats field in stats response will now have more precision.

Testing

Called TMDS v4 task stats endpoint. The results are shown below.
Before

{
  "rx_bytes_per_sec": 44802.4609375,
  "tx_bytes_per_sec": 119103.296875
}

After (only the precision is important, values from different tests won't match as a lot of factors determine the stats).

{
  "rx_bytes_per_sec": 44806.56,
  "tx_bytes_per_sec": 119114.195
}

New tests cover the changes: no

Description for the changelog

Use float64 for network rate stats

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.