New option onlyifnotexist to only create the file when it doesn't already exists

tasks/main.yml

@@ -1,8 +1,18 @@
 ---
+- name: check if the config already exists
+  ansible.builtin.stat:
+    path: "/etc/nginx/http.d/{{ instance_name }}.conf"
+    get_mime: false
+    get_checksum: false
+    get_attributes: false
+  when: onlyifnotexist is defined and onlyifnotexist
+  register: cnf
+
 - name: configure nginx for {{ instance_name }}
   template:
     src: nginx.conf.j2
     dest: "/etc/nginx/http.d/{{ instance_name }}.conf"
     mode: 0644
+  when: onlyifnotexist is not defined or not onlyifnotexist or not cnf.stat.exists
   notify:
     - reload nginx