chore(sync): Sync speed metric

## Task summary

Create prometheus metric for sync speed

We currently have logs like:

```
synced 7681 blocks, took: 46.96 seconds, bps: 163.58 blocks/second
```

But we don't have a way to graph this speed in datadog.
The goal is to send a metric and create a chart in datadog to measure our sync speed and help us to understand if a change affects this speed in a good or bad way