docs: update design/tradeoffs doc regarding scanner vuln reports #818

[pradhans0906]

Description

Updates the tradeoffs section in the design documentation to accurately reflect copa's ability to work with or without vulnerability scanner reports.

The changes:

• Remove outdated statements about scanner report dependencies
• Clarify the package-based update model
• Maintain information about package manager dependencies and platform limitations
• Improve document structure for better readability

Changes

• Replace outdated tradeoffs content with updated, accurate information
• Add clearer section organization with numbered points
• Update description of scanner integration to reflect optional usage

Closes #818

[ashnamehrotra]

@pradhans0906 can we also add these changes to version docs starting from v0.7.0, since that was the release of the update all feature. DCO also needs to be fixed to sign-off commits.

[ashnamehrotra]

@pradhans0906 thank you! looks like the commits need sign off again for DCO check