feat(vuln): enable --vex for all targets

[knqyf263]

Description

--vex is currently available only in SBOM scanning (trivy sbom). #5439 has changed to always generate PURLs, except when generating SBOMs. It is easy to extend VEX support to other targets like container images.

Example

$ trivy image debian:11 --vex debian11.vex.csaf

Related issues

• Close Extend VEX application to container Image scanning #4767

Related PRs

• feat(vuln): include pkg identifier on detected vulnerabilities #5439

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[DmitriyLewen]

LGTM