refactor(purl): use epoch in qualifier

[DmitriyLewen]

Description

Use epoch in qualifier for OS packages.

Before:
pkg:rpm/redhat/pkgconfig@1:0.27.1-4.el7?arch=x86_64&distro=redhat-7.9

After:
pkg:rpm/redhat/[email protected]?arch=x86_64&epoch=1&distro=redhat-7.9

Related issues

• Close About purl namespace and version fields for rpm #3485

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.
• 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).