feat(metrics): emit metrics for out-of-date/missing malachite data

[gary-lgy]

What type of PR is this?

What this PR does / why we need it:

Which issue(s) this PR fixes:

Special notes for your reviewer:

[codecov]

Codecov Report

Attention: Patch coverage is 90.27778% with 7 lines in your changes missing coverage. Please review.

Project coverage is 60.61%. Comparing base (fb6d1d8) to head (5b0fc00).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
...tric/provisioner/malachite/client/client_cgroup.go	93.47%	2 Missing and 1 partial ⚠️
...tric/provisioner/malachite/client/client_system.go	81.25%	2 Missing and 1 partial ⚠️
...tric/provisioner/malachite/realtime_provisioner.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #773      +/-   ##
==========================================
- Coverage   60.78%   60.61%   -0.18%     
==========================================
  Files         603      603              
  Lines       63248    63316      +68     
==========================================
- Hits        38443    38376      -67     
- Misses      20970    21095     +125     
- Partials     3835     3845      +10     

Flag	Coverage Δ
unittest	60.61% <90.27%> (-0.18%)	⬇️

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