Add way how to override rootDir in config (eg. for container use)
diff --git a/aptly/files/aptly.conf b/aptly/files/aptly.conf
index e7b1fcb..0f891f9 100644
--- a/aptly/files/aptly.conf
+++ b/aptly/files/aptly.conf
@@ -1,6 +1,6 @@
 {%- from "aptly/map.jinja" import server with context %}
 {
-  "rootDir": "{{ server.root_dir }}",
+  "rootDir": "{{ server.get('config', {}).root_dir|default(server.root_dir) }}",
   "downloadConcurrency": 4,
   "architectures": [ {% for arch in server.architectures|default([]) %}"{{ arch }}"{% if not loop.last %},{% endif %}{% endfor %} ],
   "dependencyFollowSuggests": {{ server.dependency.follow.suggests|lower }},