PPA uploads should preserve the original component

PPA uploads are currently overridden to the main component at upload time, which effectively loses all trace of what component was actually specified in the upload.

Soyuz should override the component when publishing the upload instead, so the component is preserved in the package data.

This is most useful for un-embargoing security uploads to the private security PPA, as NEW binary uploads that don't have any ancestry can be placed in the right component in the Ubuntu archive.