feat(emqx_conf): support AAAA cluster dns record type

Ekka autocluster DNS already supports AAAA records, so it's only needed to update enum in schema.

apps/emqx_conf/src/emqx_conf_schema.erl

@@ -259,7 +259,7 @@ fields(cluster_dns) ->
             )},
         {"record_type",
             sc(
-                hoconsc:enum([a, srv]),
+                hoconsc:enum([a, aaaa, srv]),
                 #{
                     default => a,
                     desc => ?DESC(cluster_dns_record_type),

changes/ce/feat-12467.en.md

@@ -0,0 +1 @@
+Support cluster discovery using AAAA DNS record type.