unifi: Switch from nginx to Caddy

Mostly for built-in ACME support.

roles/unifi/templates/unifi.caddyfile.j2

@@ -0,0 +1,13 @@
+{{ unifi_server_name }} {
+    reverse_proxy localhost:8443 {
+        transport http {
+            tls_insecure_skip_verify
+        }
+    }
+{% if unifi_caddy_acme|d %}
+
+    tls {{ unifi_caddy_acme.email }} {
+        ca {{ unifi_caddy_acme.url }}
+    }
+{% endif %}
+}