[Bug] Reenable lint-markdown-validator as a scheduled pipeline

[vidorteg]

🐞 Bug report

Description

lint-markdown-validator was disabled in here: https://github.com/webhintio/hint/pull/5755, this bug track the work required to bring it back as a scheduled task.

Details

lint-markdown-validator was preventing .md contributions from going into the repository, this was due to two main reasons:

• Some links have already expired between the last time the script was run and today.
• There is a bug in the lint-markdown-validator tool that is including all files even changelogs.

So the recommendation is to make some changes in lint-markdown-validator and let it exclude some files through a pattern and enable a pipeline that runs the script on a TBD-time basis, this will allow us to know when some links have expired over the time. Current issues will also need to be fixed