Add GH action to find broken links in Documentation (and elsewhere?)

[mccabete]

To put in a test that finds broken links, we could add a GH Action like https://github.com/marketplace/actions/lychee-broken-link-checker to check for broken links on build; it isn't clear to me where to put this in the build process.

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Original bug report:

I've noticed that most/all of the links in the documentation that are shortcuts to other parts of the documentation tend to throw a 404 error. This doesn't seem to be true of links that are to external places.

Example

Documentation: "Adding-an-Input-Converter" redirects to this.

Next Steps

1. figure out what makes these links out of date
2. put in a test that catches expired links

[dlebauer]

The links in the original bug report post are broken, but it seems like a lot (prob. not all!) of this has been fixed.

To put in a test that finds broken links, we could add a GH Action like https://github.com/marketplace/actions/lychee-broken-link-checker to check for broken links on build; it isn't clear to me where to put this in the build process.

[infotroph]

I support automated link checking, with the caveat that any "hit a bunch of external links" task is going to be slower than we think and will see lots of transient failures even from basically-working sites.

I vote we put this outside the build process, running on a set schedule (weekly?) rather than every PR and opening issues for (repeated?) failures rather than breaking the build.
Operationally, this means it should be implemented in a new file named something like .github/workflows/check-links.yml and its first 10 lines should be similar to .github/workflows/ci-weekly.yml.

[Sweetdevil144]

Would this help : #3269 ?