Support for `--timestamp` on x-axis

[myartsev]

Hey! this is really neat =)

Would be nice to have timestamp support on the x-axis.

Command:
vmstat --timestamp --unit m 1

Sample output:

procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- -----timestamp-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st                 UTC
 0  0      0   1270     75    608    0    0    96   113  193 1064 15  2 83  0  0 2023-01-24 10:27:12
 0  0      0   1270     75    608    0    0     0     0   62   95  0  0 100  0  0 2023-01-24 10:27:13

I know it's been 7 years since you last updated this, but if you're feeling up for it!