Implemented helper role docker-central-database and refactored code

roles/docker-bluesky/tasks/main.yml

@@ -53,5 +53,5 @@
 - name: add docker-compose.yml
   template: 
     src:  docker-compose.yml.j2
-    dest: "{{docker_compose_instance_directory}}docker-compose.yml"
+    dest: "{{docker_compose.directories.instance}}docker-compose.yml"
   notify: docker compose project build and setup

roles/docker-bluesky/vars/main.yml

@@ -1,8 +1,8 @@
 application_id:               "bluesky"
-social_app_path:              "{{ docker_compose_instance_directory }}/social-app"
+social_app_path:              "{{ docker_compose.directories.instance }}/social-app"
 
 # This should be removed when the following issue is closed:
 # https://github.com/bluesky-social/pds/issues/52
-pdsadmin_folder_path:         "{{ docker_compose_instance_directory }}/pdsadmin"
+pdsadmin_folder_path:         "{{ docker_compose.directories.instance }}/pdsadmin"
 pdsadmin_file_path:           "{{pdsadmin_folder_path}}/pdsadmin"
 pdsadmin_temporary_tar_path:  "/tmp/pdsadmin.tar.gz"