Add CI job that checks if CIDs, URIs and content-paths resolve

[lidel]

Inspired by https://github.com/ipfs/ipfs-docs/pull/775

Rough idea: add a CI job that finds CIDs and URIs in text files and checks if they resolve.

Things we could check:

• CIDs (check every word that starts with Qm or a multibase prefix
• content-paths /ipfs/{valid-cid} /ipns/{valid-libp2p-key-or-dnslink}
  • DNSLink presence should be validated, unless the name ends with example.com|net|org
• URIs ipfs:// and ipns:// (same rules as for content paths

Ideally:

• check would be run on every PR, but check only modified files
• run once a week and open an issue for every file that has identifier that does not resolve

[yusefnapora]

This sounds like a job for Filecorgi 😄

We should be able to rewrite IPFS cids & URIs as gateway links and use the existing external link checker that @johndmulhausen wired up.

Plan so far: @johndmulhausen is going to wire up Filecorgi to this repo, and I'll work on the CID checker script.