feat(restic): Add restic backup maintenance stack

Sets up regular backup maintenance for a restic (S3) backend, and
enables global variables for other roles to use for their individual
backup. Example found in nextcloud role.

roles/restic/meta/main.yml

@@ -0,0 +1,11 @@
+---
+galaxy_info:
+  author: Marty Oehme
+  description: Installs a restic-based backup maintenance stack. Only supports S3 atm.
+  license: GPL-3.0-only
+  min_ansible_version: "2.9"
+  galaxy_tags: []
+
+dependencies:
+  - docker-swarm
+  - caddy_id