Improve template label checks

[prymitive]

Add more test cases and improve logic

[codecov-commenter]

Codecov Report

Merging #78 (b92428f) into main (8b79532) will increase coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #78      +/-   ##
==========================================
+ Coverage   75.18%   75.28%   +0.09%     
==========================================
  Files          59       59              
  Lines        3377     3390      +13     
==========================================
+ Hits         2539     2552      +13     
  Misses        730      730              
  Partials      108      108              

Impacted Files	Coverage Δ
internal/checks/alerts_template.go	91.84% <100.00%> (ø)
internal/parser/utils/aggregation.go	63.41% <100.00%> (+16.98%)	⬆️

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