[Minor] Rbl: Add `content_urls` attribute

src/plugins/lua/rbl.lua

       ignore_ip = rule.no_ip,
       need_images = rule.images,
       need_emails = false,
+      need_content = rule.content_urls or false,
       esld_limit = esld_lim,
       no_cache = true,
     }
   process_script = ts.string:is_optional(),
   emails_delimiter = ts.string:is_optional(),
   ignore_defaults = ts.boolean:is_optional(),
+  content_urls = ts.boolean:is_optional(),
   disable_monitoring = ts.boolean:is_optional(),
   symbols_prefixes = ts.map_of(ts.string, ts.string):is_optional(),
 }