(#24) Filter of subject length

[llorllale]

This PR is for #24:

• Add subject-len filter

[codecov]

Codecov Report

Merging #25 into master will increase coverage by 1.42%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #25      +/-   ##
==========================================
+ Coverage    86.2%   87.62%   +1.42%     
==========================================
  Files           4        4              
  Lines          87       97      +10     
==========================================
+ Hits           75       85      +10     
  Misses          6        6              
  Partials        6        6

Impacted Files	Coverage Δ
internal/issues/filters.go	89.74% <100%> (+3.53%)	⬆️

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