Add support for RPM distros in url2purl and purl2ulrl

[pombredanne]

This should include RHEL, Fedora, SUSE, CentOS and Rocky Linux/CIQ

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@pombredanne http://dl.rockylinux.org/vault/centos/8.5.2111/AppStream/x86_64/kickstart/Packages/dejavu-lgc-sans-fonts-2.35-7.el8.noarch.rpm yields this PURL: pkg:generic/dejavu-lgc-sans-fonts-2.35-7.el8.noarch.rpm
It should instead return a proper RPM PURL.

@tdruez

from packageurl.contrib import url2purl

>>> str(url2purl.get_purl("http://dl.rockylinux.org/vault/centos/8.5.2111/AppStream/x86_64/kickstart/Packages/dejavu-lgc-sans-fonts-2.35-7.el8.noarch.rpm "))

'pkg:generic/dejavu-lgc-sans-fonts-2.35-7.el8.noarch.rpm?download_url=http://dl.rockylinux.org/vault/centos/8.5.2111/AppStream/x86_64/kickstart/Packages/dejavu-lgc-sans-fonts-2.35-7.el8.noarch.rpm%20'

[tdruez]

@pombredanne Could you provide the list of input URLs and their expected PURLs?