Improve the naming of metrics

Instead of:
```
neogo_rpc_traverseiterator_time_count 1200
neogo_rpc_unsubscribe_time_count 130
```

Something like this:
```
neogo_rpc_requests_total{api="traverseiterator"} 1200
neogo_rpc_requests_total{api="unsubscribe"} 130
```

This will make it easier to monitor these metrics.