docker-compose.yml.j2: update the usage of 'topic' parameter

This change is interesting due to the deprecation of the 'topics'
parameter.

waku-org/nwaku#1727

templates/docker-compose.yml.j2

@@ -47,7 +47,9 @@ services:
       --keep-alive={{ nim_waku_keep_alive | to_json }}
       --max-connections={{ nim_waku_p2p_max_connections }}
       --dns4-domain-name={{ nim_waku_dns4_domain_name }}
-      --topics='{{ nim_waku_topics | join(" ") }}'
+{% for topic in nim_waku_topics %}
+      --topic='{{ topic }}'
+{% endfor %}
 {% for protected_topic in nim_waku_protected_topics %}
       --protected-topic='{{ protected_topic | mandatory }}'
 {% endfor %}