Add the ability to manually map packages with security advisories

[javihernandez]

Currently, mapping of packages and security advisories is done in a semi-automatic way. This is, upon insertion of an upstream security advisory, we already know the packages that fix the advisory. Since we want to be able to create security advisories from scratch, we need to provide a way to add any package that can be found in ALBS.

• Ideally, we should be able to add one or many builds
• Individual package addition/removal would be potentially required - Need to double check
• Need to be able to add/update/delete mappings at any time