Add support for collecting sysstat metrics

[stone]

Collect metrics both as text and as svg graphs for today and two days back.

Example sar output:

--------------------------------
Item 150: sar -A
--------------------------------
Linux 4.18.0-553.22.1.el8_10.x86_64 (localhost) 	10/09/24 	_x86_64_	(1 CPU)

00:00:06        CPU      %usr     %nice      %sys   %iowait    %steal      %irq     %soft    %guest    %gnice     %idle
00:10:06        all      4.75      1.01     11.93      2.38      1.87      1.28      1.56      0.00      0.00     75.22
00:10:06          0      4.75      1.01     11.93      2.38      1.87      1.28      1.56      0.00      0.00     75.22
00:20:06        all      4.49      0.00      2.16      0.04      0.48      0.88      0.43      0.00      0.00     91.52
00:20:06          0      4.49      0.00      2.16      0.04      0.48      0.88      0.43      0.00      0.00     91.52
...

Example sadf generated SVG: