[Dovecot] Enable sieve vacation seconds not just for global scripts

data/conf/dovecot/dovecot.conf

@@ -329,6 +329,7 @@ plugin {
   quota_warning2 = storage=80%% quota-warning 80 %u
   sieve_pipe_bin_dir = /usr/local/lib/dovecot/sieve
   sieve_global_extensions = +vnd.dovecot.pipe +vnd.dovecot.execute +vacation-seconds
+  sieve_extensions = +vacation-seconds
   sieve_max_script_size = 1M
   sieve_max_redirects = 30
   sieve_quota_max_scripts = 0