Validate all URLs

[github-actions]

Checked 188 URLs out of which 4 is/are invalid:
http://www.gnu.org/licenses/ : Too Many Requests
https://github.com/cockpit-project/cockpit/blob/main/doc/protocol.md#command-init : Too Many Requests
https://github.com/patternfly/patternfly-react/blob/v5/packages/react-templates/src/components/Select/TypeaheadSelect.tsx : Too Many Requests
https://stackoverflow.com/questions/26634616/filereader-upload-same-file-again-not-working : Forbidden

[martinpitt]

We need to re-think our URL checker. With GitHub we can probably do authenticated requests with a token to get around the rate limits. The workflow already sets it up, but tools/urls-check does not actually use it. We also need to check what's up with gnu.org -- the /licenses URL certainly occurs umpteen times, but don't we deduplicate that? We only have two Stackoverflow URLs, may have to stop checking them when they permanently restricted scraper access.

[jelly]

If we are re-thinking this we could try to use a standard tool such as lychee has a github action and supports a GH token.

[tomasmatus]

lychee seems to work, we could use it something like this:

lychee --extensions md,js,jsx,ts,tsx,css,scss,html,txt,py --scheme http --scheme https -- $(pwd)/pkg

gnu.org most likely blocks scrapers because neither lychee can verify the link is working. Other links mentioned here went green.

note that we'll need to specify the file extensions as by default it only checks for txt, html and markdown files

[Venefilyn]

Related to cockpit-project/cockpit-project.github.io#819

[mvollmer]

Reworking of the link checker happens in cockpit-project/cockpit-project.github.io#819. All links mentioned in this issue do work.