Disable automatic removal of debs after install

apt (1.2~exp1) experimental; urgency=medium

  [ Automatic removal of debs after install ]
  After packages are successfully installed by apt(8),
  the corresponding .deb package files will be
  removed from the /var/cache/apt/archives cache directory.

  This can be changed by setting the apt configuration option
    "APT::Keep-Downloaded-Packages" to "true". E.g:

  # echo 'APT::Keep-Downloaded-Packages "true";' \
      > /etc/apt/apt.conf.d/01keep-debs

  Please note that the behavior of apt-get is unchanged. The
  downloaded debs will be kept in the cache directory after they
  are installed.

Disabling this would be nice for users who use apt to preseed their persistent APT cache.

Feature Branch: bugfix/10958-disable-automatic-removal-of-debs

Parent Task: #14570 (closed)

Original created by @intrigeri on 10958 (Redmine)