Add option to configure knot server identity

roles/knot/defaults/main.yml

@@ -3,6 +3,7 @@
 knot_server_rundir: /run/knot
 knot_server_user: knot
 knot_server_group: knot
+knot_server_identity: "{{ ansible_hostname }}"
 knot_server_listen:
   - "::@53"
   - "0.0.0.0@53"

roles/knot/templates/etc/knot/knot.conf.j2

@@ -5,6 +5,7 @@
 server:
   rundir: "{{ knot_server_rundir }}"
   user: "{{ knot_server_user }}:{{ knot_server_group }}"
+  identity: "{{ knot_server_identity }}"
 {% for addr in knot_server_listen %}
   listen: "{{ addr }}"
 {% endfor %}