feat(zone.xml): allow to rate limit 'accept' in rich rules

The current rich_rule macro is supporting to set if the connection
should be accepted or rejected or dropped but doesn't support setting
rate limiting in the 'accept' case. Add code for that.

Signed-off-by: Arnaud Patard <apatard@hupstream.com>

firewalld/files/zone.xml

     <audit>{%- if 'limit' in rule.audit %} <limit value="{{ rule.audit.limit }}"/>{%- endif %}</audit>
   {%- endif %}
   {%- if 'accept' in rule %}
-    <accept/>
+    <accept>{%- if rule.accept is mapping and 'limit' in rule.accept %} <limit value="{{ rule.accept.limit }}"/>{%- endif %}</accept>
   {%- endif %}
   {%- if 'reject' in rule %}
     <reject{%- if 'type' in rule.reject %} type="{{ rule.reject.type }}"{%- endif %} />

test/integration/default/controls/zones_spec.rb

           <source-port port="4444" protocol="tcp" />
           <rule family="ipv4">
             <source address="8.8.8.8/24" />
-            <accept/>
+            <accept></accept>
           </rule>
           <rule family="ipv4">
             <source ipset="fail2ban-ssh" />
           <rule>
             <source ipset="fail2ban-ssh" />
             <service name="ssh" />
-            <accept/>
+            <accept></accept>
           </rule>
           <rule>
             <source ipset="other-ipset" />
             <service name="ssh" />
-            <accept/>
+            <accept></accept>
           </rule>
         </zone>
       ZONE_XML