fix: default value for max_conn_rate etc should be set to infinity

Before this commit the default value for the fields max_conn_rate,
messages_rate and bytes_rate were not set. This is fixed by setting the
default value to infinity. This breaks the corresponding dashboard
fields (they can not be edited) so the dashboard also needs to be
updated.

Fixes:
https://emqx.atlassian.net/browse/EMQX-12514

apps/emqx/src/emqx_limiter/src/emqx_limiter_schema.erl

@@ -215,6 +215,7 @@ short_paths_fields(Importance) ->
             ?HOCON(rate_type(), #{
                 desc => ?DESC(Name),
                 required => false,
+                default => infinity,
                 importance => Importance,
                 example => Example
             })}

apps/emqx_management/test/emqx_mgmt_api_listeners_SUITE.erl

@@ -418,6 +418,35 @@ t_update_listener_zone(_Config) ->
     ?assertMatch({error, {_, 400, _}}, request(put, Path, [], AddConf1)),
     ?assertMatch(#{<<"zone">> := <<"zone1">>}, request(put, Path, [], AddConf2)).
 
+t_update_listener_max_conn_rate({init, Config}) ->
+    Config;
+t_update_listener_max_conn_rate({'end', _Config}) ->
+    ok;
+t_update_listener_max_conn_rate(_Config) ->
+    ListenerId = <<"tcp:default">>,
+    Path = emqx_mgmt_api_test_util:api_path(["listeners", ListenerId]),
+    Conf = request(get, Path, [], []),
+    %% Check that default is infinity
+    ?assertMatch(#{<<"max_conn_rate">> := <<"infinity">>}, Conf),
+    %% Update to infinity
+    UpdateConfToInfinity = Conf#{<<"max_conn_rate">> => <<"infinity">>},
+    ?assertMatch(
+        #{<<"max_conn_rate">> := <<"infinity">>},
+        request(put, Path, [], UpdateConfToInfinity)
+    ),
+    %% Update to 42/s
+    UpdateConfTo42PerSec = Conf#{<<"max_conn_rate">> => <<"42/s">>},
+    ?assertMatch(
+        #{<<"max_conn_rate">> := <<"42/s">>},
+        request(put, Path, [], UpdateConfTo42PerSec)
+    ),
+    %% Update back to infinity
+    UpdateConfToInfinity = Conf#{<<"max_conn_rate">> => <<"infinity">>},
+    ?assertMatch(
+        #{<<"max_conn_rate">> := <<"infinity">>},
+        request(put, Path, [], UpdateConfToInfinity)
+    ).
+
 t_delete_nonexistent_listener(Config) when is_list(Config) ->
     NonExist = emqx_mgmt_api_test_util:api_path(["listeners", "tcp:nonexistent"]),
     ?assertMatch(