New script for generating the RSS feeds for security announcements DSA

Hi all,

I've added a new feature to the script english/security/mk-dsa-dla-list
which can now create the rdf files from the DSA list provided
by the security team on salsa.debian.org.
It does not need to parse the .wml and .data files in our webwml repository.

This is a next step to get rid of manual adding the security
announcements to the web page.

Currently the new feeds are temporarily available at

https://www.debian.org/security/newdsa-long.rdf
https://www.debian.org/security/newdsa.rdf

Please test if they work for you. If everything is OK, I like to
replace the current versions of the feeds with the new ones. The URLs
will remain stable and are these:

https://www.debian.org/security/dsa
https://www.debian.org/security/dsa-long


The same is possible for the DLAs, which is not yet enabled.