Update the existing importers to use the reference type

[ziadhany]

issue: #1487
related pull request: #1518

The importer list that required an update:

• nvd,
• github
• gitlab
• npm
• pypa
• nginx
• pysec
• alpine_linux
• openssl
• redhat
• debian
• postgresql
• archlinux
• ubuntu
• debian_oval
• retiredotnet
• apache_httpd
• mozilla
• gentoo
• istio
• project_kb_msr2019
• suse_scores
• elixir_security
• apache_tomcat
• xen
• ubuntu_usn
• fireeye
• apache_kafka
• oss_fuzz
• ruby
• github_osv