compoent purl is not download url

in `RedHatSBomGenerator.java`, the method to get component purl is by parsing cmd output from `yumdownloader --urls "softwarename"`, which returns http url to download the rpm, but that's not purl.
purl definition is here: https://github.com/package-url/purl-spec

Furthermore, `yumdownloader --urls` seems to return availabe package download url rather than installed package download url, so it's not accurate.

Read RedHatSBomGenerator.java and trace the method that parses yumdownloader --urls output. Compare the returned download URL and package source with the package-url specification, and determine how installed-package information is available. Done means component purl values follow the specification and do not incorrectly use an available package download URL.

Written by the indexing model from the issue text.