fix(ynh_config): SMTP enable

With YNH 11.1 the smtp relay isn't enabled by default. It needs to be enabled first or you get this EM:

Traceback (most recent call last):
  File "/usr/bin/yunohost", line 77, in <module>
    yunohost.cli(
  File "/usr/lib/python3/dist-packages/yunohost/__init__.py", line 41, in cli
    ret = moulinette.cli(
  File "/usr/lib/python3/dist-packages/moulinette/__init__.py", line 111, in cli
    Cli(
  File "/usr/lib/python3/dist-packages/moulinette/interfaces/cli.py", line 507, in run
    ret = self.actionsmap.process(args, timeout=timeout)
  File "/usr/lib/python3/dist-packages/moulinette/actionsmap.py", line 584, in process
    return func(**arguments)
  File "/usr/lib/python3/dist-packages/yunohost/log.py", line 410, in func_wrapper
    result = func(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/yunohost/settings.py", line 87, in settings_set
    return settings.set(key, value, args, args_file, operation_logger=operation_logger)
  File "/usr/lib/python3/dist-packages/yunohost/utils/config.py", line 424, in set
    self._ask()
  File "/usr/lib/python3/dist-packages/yunohost/utils/config.py", line 736, in _ask
    questions = ask_questions_and_parse_answers(
  File "/usr/lib/python3/dist-packages/yunohost/utils/config.py", line 1609, in ask_questions_and_parse_answers
    new_values = question.ask_if_needed()
  File "/usr/lib/python3/dist-packages/yunohost/utils/config.py", line 901, in ask_if_needed
    if self.visible and not evaluate_simple_js_expression(
  File "/usr/lib/python3/dist-packages/yunohost/utils/config.py", line 190, in evaluate_simple_js_expression
    return evaluate_simple_ast(node, context)
  File "/usr/lib/python3/dist-packages/yunohost/utils/config.py", line 78, in evaluate_simple_ast
    return context[node.id]
KeyError: 'smtp_relay_enabled'

Some extra info here