chore: update to latest final 2.1.0

[spiffcs]

📑 Description

It looks like the 2.1.0 schema was finalized and exists here.

Documents generated with go-sarif using the old schema rtm in the schema field will fail Microsoft's schema validation found here:
https://sarifweb.azurewebsites.net/

The diff between rtm and main is immaterial and only consists of description updates.

This change should make the schema field of the generated document valid with upstream tooling =)

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

[spiffcs]

Also happy to update the URL to any other one you might deem more appropriate =)

[spiffcs]

@owenrumney Let me know if there is anything else you need for this PR - happy to make any changes or updates!

[owenrumney]

Thanks for this @spiffcs - I wonder if we should use https://docs.oasis-open.org/sarif/sarif/v2.1.0/errata01/os/schemas/sarif-schema-2.1.0.json for the schema as this appears to be the up-to-date one direct

[owenrumney]

thanks - I can't push to your branch but I've used the commits and used the oasis-open URL in #71

[spiffcs]

Thanks @owenrumney - sorry for missing the follow up!