feat: relax flag validation for test/monitor commands

[paulrosca-snyk]

Pull Request Submission Checklist

• Follows CONTRIBUTING guidelines
• Commit messages
  are release-note ready, emphasizing
  what was changed, not how.
• Includes detailed description of changes
• Contains risk assessment (Low | Medium | High)
• Highlights breaking API changes (if applicable)
• Links to automated tests covering new functionality
• Includes manual testing instructions (if necessary)
• Updates relevant GitBook documentation (PR link: ___)
• Includes product update to be announced in the next stable release notes

What does this PR do?

Relaxes the flag validation for snyk test and snyk monitor so that the command can be routed to the new flow (e.g reachability) even when an unknown flag is being passed.

Where should the reviewer start?

How should this be manually tested?

Running snyk test --reachability --foo-bar should return the vulnerability information enriched with reachability signals.

What's the product update that needs to be communicated to CLI users?

N/A

Risk assessment (Low | Medium | High)?

Low. This only impacts customers which use the new testing flow, and the impact should be positive.