fix(config): enforce root key name to be a binary (raw config)

Fixes this flaky test:
https://github.com/emqx/emqx/actions/runs/5134910014/jobs/9239826162#step:8:1299

```
=ERROR REPORT==== 31-May-2023::16:16:10.710969 ===
    exception: error
    key_path: [listeners,tcp,default,authentication]
    module: emqx_schema
    msg: change_config_crashed
    reason: {config_not_found,[<<"listeners">>,<<"tcp">>,<<"default">>,
                               <<"authentication">>]}
    stacktrace: [{emqx_utils_maps,deep_get,2,
                     [{file,
                          "/__w/emqx/emqx/source/apps/emqx_utils/src/emqx_utils_maps.erl"},
                      {line,49}]},
                 {emqx_config_handler,return_change_result,2,
                     [{file,
                          "/__w/emqx/emqx/source/apps/emqx/src/emqx_config_handler.erl"},
                      {line,456}]},
                 {emqx_config_handler,check_and_save_configs,7,
                     [{file,
                          "/__w/emqx/emqx/source/apps/emqx/src/emqx_config_handler.erl"},
                      {line,284}]},
                 {emqx_config_handler,handle_update_request,4,
                     [{file,
                          "/__w/emqx/emqx/source/apps/emqx/src/emqx_config_handler.erl"},
                      {line,195}]},
                 {emqx_config_handler,handle_call,3,
                     [{file,
                          "/__w/emqx/emqx/source/apps/emqx/src/emqx_config_handler.erl"},
                      {line,124}]},
                 {gen_server,try_handle_call,4,
                     [{file,"gen_server.erl"},{line,1149}]},
                 {gen_server,handle_msg,6,
                     [{file,"gen_server.erl"},{line,1178}]},
                 {proc_lib,init_p_do_apply,3,
                     [{file,"proc_lib.erl"},{line,240}]}]
    update_req: {{update,
                     {create_authenticator,'tcp:default',
                         #{backend => built_in_database,enable => true,
                           mechanism => password_based}}},
                 #{rawconf_with_defaults => true}}
```

Which was cause because there were both binary and atom `listeners`
keys in the `persistent_term` storage:

```erlang
%% persistent_term:get()
{{emqx_config,raw_conf,<<"listeners">>},
 #{<<"ssl">> =>
       #{<<"default">> => ...
...
{{emqx_config,raw_conf,listeners},#{}},
```

... and the atom one was winning when fetching the whole config with
`emqx_config:get_raw([])`.

apps/emqx/src/emqx_config.erl

@@ -299,14 +299,15 @@ get_raw(KeyPath, Default) -> do_get_raw(KeyPath, Default).
 put_raw(Config) ->
     maps:fold(
         fun(RootName, RootV, _) ->
-            ?MODULE:put_raw([RootName], RootV)
+            ?MODULE:put_raw([bin(RootName)], RootV)
         end,
         ok,
         hocon_maps:ensure_plain(Config)
     ).
 
 -spec put_raw(emqx_utils_maps:config_key_path(), term()) -> ok.
-put_raw(KeyPath, Config) ->
+put_raw(KeyPath0, Config) ->
+    KeyPath = [bin(K) || K <- KeyPath0],
     Putter = fun(Path, Map, Value) ->
         emqx_utils_maps:deep_force_put(Path, Map, Value)
     end,

apps/emqx/test/emqx_authentication_SUITE.erl

@@ -297,6 +297,7 @@ t_update_config({init, Config}) ->
     ];
 t_update_config(Config) when is_list(Config) ->
     emqx_config_handler:add_handler([?CONF_ROOT], emqx_authentication),
+    ok = emqx_config_handler:add_handler([listeners, '?', '?', ?CONF_ROOT], emqx_authentication),
     ok = register_provider(?config("auth1"), ?MODULE),
     ok = register_provider(?config("auth2"), ?MODULE),
     Global = ?config(global),

apps/emqx/test/emqx_crl_cache_SUITE.erl

@@ -279,7 +279,7 @@ does_module_exist(Mod) ->
 
 clear_listeners() ->
     emqx_config:put([listeners], #{}),
-    emqx_config:put_raw([listeners], #{}),
+    emqx_config:put_raw([<<"listeners">>], #{}),
     ok.
 
 assert_http_get(URL) ->