feat: add --distro flag to manually specify OS distribution for vulnerability scanning

[knqyf263]

Description

Adding --distro. See #8065 for details.

$ trivy image alpine:3.20 --scanners vuln --distro alpine/edge
2024-12-09T11:55:13+04:00       INFO    [vuln] Vulnerability scanning is enabled
2024-12-09T11:55:16+04:00       INFO    Overriding detected OS with provided distro     detected="alpine/3.20.3" provided="alpine/edge"
2024-12-09T11:55:16+04:00       INFO    Detected OS     family="alpine" version="edge"
2024-12-09T11:55:16+04:00       INFO    [alpine] Detecting vulnerabilities...   os_version="edge" repository="" pkg_num=14
2024-12-09T11:55:16+04:00       INFO    Number of language-specific files       num=0

TODOs

• Add --distro flag
• Override detected OS
• Override detected repository
• Add unit tests
• Add integration tests
• Add documentation

Related issues

• Close feat: add --distro flag to manually specify OS distribution for vulnerability scanning #8065

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