📦 Add link check action

[TechWiz-3]

Thank you for taking the time to work on a PR for Awesome-Selfhosted!

To ensure your PR is dealt with swiftly please check the following:

• Submit one item per pull request. This eases reviewing and speeds up inclusion.
• Format your submission as follows, where Demo and Clients are optional.
  Do not add a duplicate Source code link if it is the same as the main link.
  Keep the short description under 250 characters and use sentence case
  for it, even if the project's webpage or readme uses another capitalisation
  such as title case, all caps, small caps or all lowercase.
  Demo links should only be used for interactive demos, i.e. not video demonstrations.
  - [Name](http://homepage/) - Short description, under 250 characters, sentence case. ([Demo](http://url.to/demo), [Source Code](http://url.of/source/code), [Clients](https://url.to/list/of/related/clients-or-apps)) `License` `Language`
• Additions that depend on proprietary services outside the user's control must be marked ⚠.
  - [Name](http://homepage/) `⚠` - Short description, under 250 characters, sentence case. ([Demo](http://url.to/demo), [Source Code](http://url.of/source/code), [Clients](https://url.to/list/of/related/clients-or-apps)) `License` `Language`
• Additions that are not Free software must be added to non-free.md and have the license set to ⊘ Proprietary
• Additions are inserted preserving alphabetical order.
• Additions are not already listed at any of awesome-sysadmin, awesome-analytics, staticgen.com, staticsitegenerators.net.
• The Language tag is the main server-side requirement for the software. Don't include frameworks or specific dialects.
• Any license you add is in our list of licenses.
• You have searched the repository for any relevant issues or PRs, including closed ones.
• Any category you are creating has the minimum requirement of 3 items.
  If not, your addition may be inserted into Misc/Other.
• Any software project you are adding to the list is actively maintained.
• The pull request title is informative, unlike "Update README.md".
  Suggested titles: "Add aaa to bbb" for adding software aaa to section bbb,
  "Remove aaa from bbb" for removing, "Fix license for aaa", etc.

PR Info

In this PR, I have added a workflow which checks links and fails if any of them are broken.

Disclaimer: this action is my own action, the repo is here. Because of the huge volume of links, I'm using the 'fast' version/branch which simply requires a github token to be stored as TOKEN as a repo secret (for requests to the github api to avoid rate-limits).

You can view the logs of the workflow on my fork here. 31 links were found to be broken.

Let me know if you'd like me to change anything, any feedback is appreciated either way :)

[nodiscc]

See #1038 and related issues.