Adds automated link checking and fixes broken links

[vishnuravi]

Adds automated link checking and fixes broken links

♻️ Current situation & Problem

This PR adds automated link checking of all markdown files and fixes broken links. The check will run on all pull requests and automatically on the first of each month at midnight.

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[codecov]

Codecov Report

Merging #15 (32d4747) into main (58f79a2) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #15   +/-   ##
=======================================
  Coverage   91.65%   91.65%           
=======================================
  Files           6        6           
  Lines         431      431           
=======================================
  Hits          395      395           
  Misses         36       36           

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[PSchmiedmayer]

Thank you for the fix @vishnuravi!

Similarly to Spezi-Storage: Can we use the chance to directly add the URL link check to this PR?

I would suggest that we add this for every PR and in addition maybe as automated checks that run every month, e.g., on the first of the month? We should make this consistent across the different Spezi Modules as we update them with different PRs that make documentation or functionality-related changes.

https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#schedule

[PSchmiedmayer]

Thank you; looks great! 🚀