[SYS] Refine json buffer maximum size (#2005)

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

main/User_config.h

@@ -158,7 +158,7 @@
 #  if MQTT_SECURE_DEFAULT
 #    define JSON_MSG_BUFFER_MAX 2048 // Json message buffer size increased to handle certificate changes through MQTT, used for the queue and the coming MQTT messages
 #  else
-#    define JSON_MSG_BUFFER_MAX JSON_MSG_BUFFER
+#    define JSON_MSG_BUFFER_MAX 898 // Minimum size for the cover MQTT discovery message
 #  endif
 #endif
 

main/ZmqttDiscovery.ino

@@ -240,7 +240,7 @@ 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<1024> jsonBuffer;
+  StaticJsonDocument<JSON_MSG_BUFFER_MAX> jsonBuffer;
   JsonObject sensor = jsonBuffer.to<JsonObject>();
 
   // If a component cannot render it's state (f.i. KAKU relays) no state topic