feat(linkding): Add linkding stack

Bookmarking software similar to shaarli but a bit more featureful. And
not written in php, thankfully.

roles/linkding/defaults/main.yml

@@ -0,0 +1,19 @@
+---
+linkding_version: latest-plus # plus contains self-archiving possibilities with singlefile
+
+linkding_upstream_file_dir: "{{ docker_stack_files_dir }}/{{ stack_name }}"
+
+linkding_use_https: true
+
+linkding_autoupdate: true
+
+# the subdomain link linkding will be reachable under
+subdomain_alias: ld
+
+# initial superuser creation
+linkding_username: linkdinger
+linkding_password: linkdingerpass123
+
+# should we back up the data?
+linkding_backup_enable: true
+linkding_backup_cron: 0 45 3 * * *