[DOC] update design/tradeoffs doc regarding scanner vuln reports

[sozercan]

What kind of documentation improvement is needed?

Incorrect or outdated information

What is the change that is needed?

This doc can be improved since copa doesn't have to rely on scanner reports anymore

https://project-copacetic.github.io/copacetic/website/design#tradeoffs

Are you willing to submit PRs to contribute to documentation?

• [ ] Yes, I am willing to implement it.

[pradhans0906]

Please assign to me @sozercan, will update the docs