Feature/477 add iowait to cpu

Describe the MR

This MR adds a number of detailed metrics to the CPU probe:

• CPUResultBusy : % of time spent running (sum of all "non-idle" times)
• CPUResultIdle : % of time spent idle
• CPUResultUser : % of time spent in user mode
• CPUResultSystem : % of time spent in system mode, which is the time spent executing kernel code
• CPUResultNice : % of time spent in user mode with low priority (nice)
• CPUResultIowait : % of time waiting for I/O to complete
• CPUResultIrq : % of time servicing interrupts
• CPUResultSoftirq : % of time servicing softirqs

Why was this MR needed?

Feature request demanding (at least) IOWait.

Extra-care points?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• CHANGELOG updated
• Unit Tests added/updated

What are the relevant issue numbers?

Closes #477 (closed)

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