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/defaults/main.yml

@@ -0,0 +1,13 @@
+---
+
+caddy_version: alpine
+caddy_caddyfile_dir: "{{ docker_stack_files_dir }}/caddy"
+
+caddy_use_debug: no
+
+caddy_use_https: yes
+caddy_tls_use_staging: no
+# caddy_email: your@email.here
+
+# sets up a quick test server on port 80 to see if the container is set up correctly
+caddy_create_test_file_server: no