feat: add --no-color flag to disable colored output

[goutham-hari]

Description

Adds a global --no-color flag to disable colored terminal output across Trivy.

Related issues

Closes #1091

Checklist

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• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
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• I've included a "before" and "after" example to the description (if the PR is a user interface change).

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