report: add `apt-cache policy` to list recognized APT sources

report: add `apt-cache policy` to list recognized APT sources

with their details as well as pinned packages. Omit the "origin"
lines, as their value is already visible in the URLs.

 # apt-cache policy ...
 Package files:
  100 /var/lib/dpkg/status
      release a=now
  500 https://enterprise.proxmox.com/debian/pve bookworm/pve-enterprise amd64 Packages
      release o=Proxmox,a=stable,n=bookworm,l=Proxmox VE Enterprise Debian Repository,c=pve-enterprise,b=amd64
 ...
 Pinned packages:
      intel-microcode -> 3.20231114.1~deb12u1 with priority 1234

Signed-off-by: Alexander Zeidler <a.zeidler@proxmox.com>