ci: add markdown link checker workflow and configuration

[deependujha]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Fixes #128

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84%. Comparing base (d3e3247) to head (0cb051b).
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Additional details and impacted files

@@         Coverage Diff         @@
##           main   #168   +/-   ##
===================================
  Coverage    84%    84%           
===================================
  Files        12     12           
  Lines       511    511           
===================================
  Hits        430    430           
  Misses       81     81           

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