feat(linkding): Add linkding stack

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

roles/linkding/meta/main.yml

@@ -0,0 +1,11 @@
+---
+galaxy_info:
+  author: Marty Oehme
+  description: Installs linkding as a docker stack service
+  license: GPL-3.0-only
+  min_ansible_version: "2.9"
+  galaxy_tags: []
+
+dependencies:
+  - docker-swarm
+  - caddy_id