[SYS] Fix ESP8266 discovery publications (#2100)

Co-authored-by: Florian <1technophile@users.noreply.github.com>

main/ZmqttDiscovery.ino

@@ -242,7 +242,7 @@ void createDiscovery(const char* sensor_type,
                      const char* payload_available, const char* payload_not_available, bool gateway_entity, const char* cmd_topic,
                      const char* device_name, const char* device_manufacturer, const char* device_model, const char* device_id, bool retainCmd,
                      const char* state_class, const char* state_off, const char* state_on, const char* enum_options, const char* command_template) {
-  StaticJsonDocument<JSON_MSG_BUFFER_MAX> jsonBuffer;
+  StaticJsonDocument<JSON_MSG_BUFFER> jsonBuffer;
   JsonObject sensor = jsonBuffer.to<JsonObject>();
 
   // If a component cannot render it's state (f.i. KAKU relays) no state topic