(Closes #2638) add new linkspector workflow

[arporter]

No description provided.

[arporter]

Addresses the persistent false positive in the link checking by moving to 'linkspector' instead of markdown link checker. They are both running in parallel in this PR but once the reviewer is happy I propose removing 'markdown-link-checker' altogether.
One for @hiker, @LonelyCat124, @TeranIvy or @sergisiso.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.86%. Comparing base (98e15d6) to head (89b9dec).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2639   +/-   ##
=======================================
  Coverage   99.86%   99.86%           
=======================================
  Files         351      351           
  Lines       48396    48396           
=======================================
  Hits        48331    48331           
  Misses         65       65           

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[sergisiso]

@arporter I agree we should move to the new tool if it's better and the new preferred way. Also I agree in removing the old check (and its config file) in this PR.

[arporter]

All green and lovely now. I remembered that I needed to update the Dev Guide so I've done that now.
Ready for another look.

[sergisiso]

@arporter All comments have been addressed, the CI issues are gone and the documentation has been updated. This is ready to merge.