Add basic nextcloud deployment

Uses php-fpm image and is served through a simple caddy server.
Automatically deploys by default and can be automatically deployed with
smtp e-mail sending and s3 primary object storage optionally if desired.

Utilizes some necessary hackery for container ordering and startup so
startup is relatively slow (takes around 2-5 minutes at least) but once
running should be stable and uninterrupted.

Implements health-checks for all involved containers.

Switch apache for php-fpm image

roles/caddy/templates/docker-stack.yml.j2

@@ -4,6 +4,12 @@ services:
   app:
     image: caddy:{{ caddy_version }}
     command: caddy run --config /etc/caddy/config.json
+    healthcheck:
+        test: ["CMD", "wget", "--quiet", "--spider", "--tries=1", "http://localhost:2019/metrics"]
+        interval: 1m
+        timeout: 10s
+        retries: 3
+        start_period: 1m
     ports:
       - "80:80"
       - "443:443"