service: Add support for template mounts

Template mounts are templated from jinja2 templates to a service name
-specific directory under /srv and bind mounted inside the container.

roles/service/tasks/validation.yaml

@@ -8,3 +8,9 @@
   ansible.builtin.fail:
     msg: "service_postgres_tag needs to be set when database type is postgres"
   when: "service_database_type == 'postgres' and service_postgres_tag is not defined"
+
+- name: Fail if template mount source doesn't end in .j2
+  ansible.builtin.fail:
+    msg: "Template mount source file name needs to end in .j2. The file {{ item.source }} of {{ service_name }} doesn't."
+  when: "item.source | split('.') | last != 'j2'"
+  loop: "{{ _service_template_mounts }}"