fix: dashboard listener cacertfile is optional

apps/emqx_dashboard/src/emqx_dashboard_listener.erl

@@ -188,7 +188,7 @@ ensure_ssl_cert(#{<<"listeners">> := #{<<"https">> := #{<<"bind">> := Bind} = Ht
     Https1 = emqx_dashboard_schema:https_converter(Https0, #{}),
     Conf1 = emqx_utils_maps:deep_put([<<"listeners">>, <<"https">>], Conf0, Https1),
     Ssl = maps:get(<<"ssl_options">>, Https1, undefined),
-    Opts = #{required_keys => [[<<"keyfile">>], [<<"certfile">>], [<<"cacertfile">>]]},
+    Opts = #{required_keys => [[<<"keyfile">>], [<<"certfile">>]]},
     case emqx_tls_lib:ensure_ssl_files_in_mutable_certs_dir(?DIR, Ssl, Opts) of
         {ok, undefined} ->
             {error, <<"ssl_cert_not_found">>};