Add basic caddy swarm role

Added caddy as swarm container. Uses templated Caddyfile which can be
set up for testing purposes for now.
Depends on docker and docker-swarm, and will keep its stuff where
docker-swarm sets itself up.

roles/caddy/templates/Caddyfile.j2

@@ -0,0 +1,26 @@
+{
+{%- if caddy_email is not none %}   
+    email {{ caddy_email }}
+{% endif %}
+
+{% if caddy_tls_use_staging is sameas true %}
+    acme_ca https://acme-staging-v02.api.letsencrypt.org/directory
+{% endif %}
+
+{% if caddy_use_debug is sameas true %}
+    debug
+{% endif %}
+
+{% if caddy_use_https is sameas false %}
+    auto_https off
+{% endif %}
+}
+
+{% if caddy_create_test_file_server is sameas true %}
+:80 {
+    file_server {
+        browse
+    }
+}
+{% endif %}
+

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

@@ -0,0 +1,22 @@
+version: "3.7"
+
+services:
+  app:
+    image: caddy:{{ caddy_version }}
+    ports:
+      - "80:80"
+      - "443:443"
+    volumes:
+      - "{{ caddy_caddyfile_dir }}:/etc/caddy"
+      - data:/data
+      - config:/config
+    networks:
+      - "{{ docker_swarm_public_network_name }}"
+
+volumes:
+  data:
+  config:
+
+networks:
+  "{{ docker_swarm_public_network_name }}":
+    external: true