link checker - fails PR if links are broken

[clubanderson]

Fix #140

[elevran]

The run failed with 4 broken links:

...
🔍 Scanning all Markdown files for broken links...
------------------------------------------------------------
📄 Checking: ./README.md

  ERROR: 3 dead links found in ./README.md !
  [✖] /docs/architecture.md → Status: 400
  [✖] /docs/dp.md → Status: 400
  [✖] /DEVELOPMENT.md → Status: 400
❌ 3 broken links in ./README.md
------------------------------------------------------------
📄 Checking: ./DEVELOPMENT.md

  ERROR: 1 dead links found in ./DEVELOPMENT.md !
  [✖] https://www.gnu.org/software/make/ → Status: 0
❌ 1 broken links in ./DEVELOPMENT.md
------------------------------------------------------------
📄 Checking: ./docs/architecture.md

✅ No broken links in ./docs/architecture.md
------------------------------------------------------------
📄 Checking: ./docs/dp.md

✅ No broken links in ./docs/dp.md
------------------------------------------------------------
📄 Checking: ./docs/create_new_filter.md

✅ No broken links in ./docs/create_new_filter.md
------------------------------------------------------------
❌ Total broken links found: 4
Error: Process completed with exit code 1.

However, upon inspection (and actually clicking on the link...) - all are valid.
We can not merge this PR as it clearly produces false positives. The 400 error code is Bad Request which suggests that the tool is faulty or misconfigured for our environment.

[elevran]

@clubanderson thanks!
this is a good check to have and would love to have it integrated. However, the tool added in this PR currently produces "false positives" and we can not merge it.

[elevran]

For the markdown failures in the README.md, it seems that the tool is handling links that GH (markdown and as a web server) process correctly.
Links to files in the local repository can be encoded using an absolute path (e.g., /DEVELOPMENT.md, and GH would interpret them based on the repo's entry point (e.g., https://github.com/llm-d/llm-d-inference-scheduler in our case). The tool seems to treat them as pure absolute path (relative to https://github.com?) and that results in the 400 response.

I'm not sure why it fails on GNU make, though. Note that the return Status code reported for the HTTP request is 0, which is not a valid 3-digit return code.

[elevran]

@clubanderson - I've made changes needed to your PR to make it pass.
PTAL and let me know what you think