apt: Make APT config options customisable

apt/defaults/main.yml

@@ -7,3 +7,6 @@ apt_repos: ['main', 'contrib', 'non-free']
 apt_sets: ['', '-updates']  # ['-backports', '-proposed-updates']
 apt_src_enable: true
 raspbian_has_no_security: false
+apt_configs:
+  - 50debconf-exec-tmp
+  - 51apt-sandbox

apt/tasks/main.yml

@@ -31,9 +31,7 @@
     owner: root
     group: root
     mode: '0644'
-  with_items:
-    - 50debconf-exec-tmp
-    - 51apt-sandbox
+  loop: "{{ apt_configs }}"
   tags:
     - config
     - apt