feat: add technical-debt metric

[dkrutskikh]

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix
[ ] New rule
[ ] Changes an existing rule
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Is there anything you'd like reviewers to focus on?

[codecov]

Codecov Report

Merging #575 (ddfdd71) into master (411c51b) will increase coverage by 0.55%.
The diff coverage is 100.00%.

❗ Current head ddfdd71 differs from pull request most recent head 29e0ffe. Consider uploading reports for the commit 29e0ffe to get more accurate results

@@            Coverage Diff             @@
##           master     #575      +/-   ##
==========================================
+ Coverage   85.79%   86.34%   +0.55%     
==========================================
  Files         227      229       +2     
  Lines        4731     4827      +96     
==========================================
+ Hits         4059     4168     +109     
+ Misses        672      659      -13     

Impacted Files	Coverage Δ
.../analyzers/lint_analyzer/metrics/metric_utils.dart	100.00% <100.00%> (ø)
...alyzers/lint_analyzer/metrics/metrics_factory.dart	100.00% <100.00%> (ø)
...ics_list/technical_debt/technical_debt_metric.dart	100.00% <100.00%> (ø)
...r/metrics/metrics_list/technical_debt/visitor.dart	100.00% <100.00%> (ø)
lib/src/analyzers/lint_analyzer/lint_analyzer.dart	93.66% <0.00%> (+5.63%)	⬆️
...zers/lint_analyzer/metrics/models/file_metric.dart	100.00% <0.00%> (+100.00%)	⬆️

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