utils.c: *default_srv_config: add configuration for min_account_age

Signed-off-by: Yonle <yonle@lecturify.net>

utils.c

@@ -29,6 +29,7 @@ static const char *default_srv_config = "{"
     "\"max_timeline_entries\": 50,"
     "\"timeline_purge_days\":  120,"
     "\"local_purge_days\":     0,"
+    "\"min_account_age\":      0,"
     "\"admin_email\":          \"\","
     "\"admin_account\":        \"\","
     "\"title\":                \"\","