Script for adding entries to 'sources.list' file

Check if entry is not exists already and add both 'deb'
and 'deb-src' entries to '/etc/apt/sources.list' file.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>
Reviewed-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Reviewed-by: Héctor Orón Martínez <hector.oron@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D7379