refine implementation of sysadvisor policies

[waynepeking348]

What type of PR is this?

Style

What this PR does / why we need it:

change the elements in sys-advisor policies to small lowercases to avoid unexpected writes

[codecov]

Codecov Report

Patch coverage: 87.23% and project coverage change: +8.62 🎉

Comparison is base (b94d82c) 42.76% compared to head (b35a461) 51.39%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   42.76%   51.39%   +8.62%     
==========================================
  Files         143      302     +159     
  Lines       23374    31175    +7801     
==========================================
+ Hits         9997    16022    +6025     
- Misses      12058    13303    +1245     
- Partials     1319     1850     +531     

Flag	Coverage Δ
unittest	51.39% <87.23%> (+8.62%)	⬆️

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

Impacted Files	Coverage Δ
pkg/agent/sysadvisor/metacache/metacache.go	84.00% <ø> (ø)
...resource/memory/headroompolicy/policy_canonical.go	78.26% <75.00%> (ø)
...urce/cpu/region/headroompolicy/policy_canonical.go	64.51% <80.00%> (ø)
...rce/cpu/region/provisionpolicy/policy_canonical.go	75.00% <80.00%> (ø)
...ware/resource/memory/headroompolicy/policy_base.go	83.33% <80.00%> (ø)
...resource/cpu/region/provisionpolicy/policy_base.go	91.30% <93.33%> (ø)
.../resource/cpu/region/headroompolicy/policy_base.go	100.00% <100.00%> (ø)

... and 222 files with indirect coverage changes

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