Provide a test signer with a self-signed certificate

[ok-nick]

It would be convenient if c2pa-web provided a test signer and certificates for quick testing during development. Perhaps a c2pa-test package would be a better fit?

[ok-nick]

Additionally, an example for creating a signer from PEMs would be immensely helpful!

[domvanrob]

Also interested in the signing procedure using the rust wrapper within this repo. It's unclear whether the current implementation is incomplete or whether I'm missing something.

[github-jira-sync-bot]

❌ Cannot export the issue. This GitHub issue is already linked to Jira issue(s): https://jira.corp.adobe.com/browse/CAI-3358