Fixes #2277: clarify fields in APT package manager configuration
Merge pull request #153 from jooooooon/bug_2277/clarify_fields_in_technique_apt_manager_settings

Fixes #2277: clarify fields in APT package manager configuration
Merge branch 'branches/rudder/2.4' into branches/rudder/2.5
Merge branch 'branches/rudder/2.5' into branches/rudder/2.6
Merge branch 'branches/rudder/2.6'