Download apt source list to map source packages for BOM and merge data

At image generation the list of build deps of each package is got and mapped to source package names. To do so, the apt cache is used, but since in target images development repositories are not enabled this process fail.

To overcome this issue, download the list of apt repositories and pass it to the script.

Also, improve the way data is merged to avoid dropping information.

https://phabricator.apertis.org/T9756

Signed-off-by: Walter Lozano walter.lozano@collabora.com