add memory usage metric

[luomingmeng]

What type of PR is this?

Enhancements

What this PR does / why we need it:

add memory usage metric

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.01% 🎉

Comparison is base (3229ded) 51.76% compared to head (2bbf057) 51.77%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #198      +/-   ##
==========================================
+ Coverage   51.76%   51.77%   +0.01%     
==========================================
  Files         436      436              
  Lines       41922    41954      +32     
==========================================
+ Hits        21701    21723      +22     
- Misses      17874    17886      +12     
+ Partials     2347     2345       -2     

Flag	Coverage Δ
unittest	51.77% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
...sysadvisor/plugin/metric-emitter/syncer/pod/pod.go	66.44% <ø> (ø)

... and 16 files with indirect coverage changes

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