fix(sbom): change error to warning for multiple OSes

[knqyf263]

Description

This PR shows a warning message for multiple OSes in SBOM rather than returning an error. It's a kind of workaround that allows KBOM scanning to be done successfully.

Before

$ trivy sbom ./sbom-k8s-cluster.json
2024-04-23T10:49:22+04:00       INFO    Vulnerability scanning is enabled
2024-04-23T10:49:22+04:00       INFO    Detected SBOM format    format="cyclonedx-json"
2024-04-23T10:49:22+04:00       FATAL   Fatal error     sbom scan error: scan error: scan failed: failed analysis: SBOM decode error: failed to decode: failed to decode components: multiple OS components are not supported

After

$ trivy sbom ./sbom-k8s-cluster.json
2024-04-23T11:06:41+04:00       INFO    Vulnerability scanning is enabled
2024-04-23T11:06:41+04:00       INFO    Detected SBOM format    format="cyclonedx-json"
2024-04-23T11:06:41+04:00       WARN    [sbom] Multiple OS components are not supported, taking the first one and ignoring the rest
2024-04-23T11:06:41+04:00       WARN    No OS package is detected. Make sure you haven't deleted any files that contain information about the installed packages.
2024-04-23T11:06:41+04:00       WARN    e.g. files under "/lib/apk/db/", "/var/lib/dpkg/" and "/var/lib/rpm"
2024-04-23T11:06:41+04:00       INFO    Detected OS     family="bottlerocket os" version="1.19.2"
2024-04-23T11:06:41+04:00       WARN    Unsupported os  family="bottlerocket os"
2024-04-23T11:06:41+04:00       INFO    Number of language-specific files       num=3
2024-04-23T11:06:41+04:00       INFO    [kubernetes] Detecting vulnerabilities...

Related issues

• Close Multiple OS components in SBOM are not supported properly #6506

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

[chen-keinan]

@knqyf263 did quick test and it look that it solve the issue