Find and add some useful workflows to the pipeline

[Zabuzard]

There are for sure some useful GH-actions workflows out there, which we could add to our pipeline (besides deploying the website).

Some things that come to my mind would be:

• [x] spelling/grammar checking
• [x] markdown validation/linter (sonar? codeql? codefactor? ...)
• [x] markdown formatting (spotless? ...)
• [x] dead link checker
• [ ] (if possibly, some sort of code checking on snippets)
• maybe more?

[Zabuzard]

Added a linter. Unfortunately, it doesnt have a super nice UI. But it works.

[Zabuzard]

added a dead-link checker

[Zabuzard]

Added a language checker based on LanguageTool

[Zabuzard]

ill see if i can find more useful stuff

[github-actions[bot]]

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[bowbahdoe]

These workflows, TBH, have been more of a PITA than anything else. I disabled the markdown lint one since there are way too many things to fix + autoformatting breaks footnotes. Will revisit if it starts to matter more or I start making a ton of meaningful mistakes