Feature: gather and show system load from logfile

[happybeing]

Use the following node log TRACE output to gather metrics for:

System:

• CPU usage
• total and free memory
• total and free swap

Node:

• memory
• virtual memory
• CPU usage
• disk: total written bytes
• disk: written bytes
• prefix

Provide horizontal bar display of:

• system CPU usage (green bar, highlight text in red when over 90%)
• node CPU usage
• system memory used/free memory (green bar, highlight text in red when over 75%)

Show node prefix in LHS panel

 TRACE 2022-01-27T13:02:57.320967Z [sn/src/node/logging/mod.rs:L71]:
     ➤ log {system=System { global CPU usage: 100.0, load average: LoadAvg { one: 119.24, five: 178.42, fifteen: 148.32 }, total memory: 67022352, free memory: 7430066, total swap: 2147479, free swap: 2128408, nb CPUs: 8, nb network interfaces: 4, nb processes: 447, nb disks: 2, nb components: 8 } print_resources_usage=false}
     ➤ Node resource usage: Process { memory: 71520, virtual_memory: 2712522752, cpu_usage: 8.668731, disk_usage: DiskUsage { total_written_bytes: 860160, written_bytes: 45056, total_read_bytes: 0, read_bytes: 0 } } prefix="000000.."

[happybeing]

I've published v0.7.3 which add system and node resource display, but leaving this open as I think it might be improved with feedback, such as changing the text colours depending on CPU load.