Track UJ node progress

[d-helios]

Motivation

Monitoring should be able to identify nodes that are too slow to join the cluster, or perhaps simply stuck.

Possible implementation

Once new node is created and scylla is started, monitoring stack should start scrapping metrics from scylla and operating system.
If new node in UJ state.

• verify network traffic - scylla_node_network_receive_bytes_total
• verify disk space utilisation - scylla_node_filesystem_total_avail_bytes

if diff for the last X minutes lower then Y over the Z minutes, trigger an alert.

[amnonh]

@d-helios luckily, I've added a metrics for a node state, scylla_node_operation_mode so we can check if a node is in joining mode for more than X minutes

[amnonh]

@d-helios note that this is monitoring only and if it's cloud related, there should be a cloud issue