Exclude values from Tuya Valve Thermostat
### Device Model

TuYa TS0601_thermostat

### Is there an existing issue for this?

- [X] I have searched the existing issues and did not find an existing issue.

### Supported by Zigbee2MQTT?

- [X] Device is supported by Zigbee2MQTT

### Missing features / functionality

Hi! The device exposes "system_mode" with values: `heat`, `auto` and `off`
I'm trying to exclude `heat` value, and only leave `auto` since heat doesn't make sense - whatever temperature you set for the heat mode, the valve will always remain opened and never clooses.

Any advice is greatly appreciated!

### HomeKit Services and Characteristics

Here's my configuration:
```json
{
    "accessories": [],
    "platforms": [
        {
            "platform": "zigbee2mqtt",
            "mqtt": {
                "base_topic": "zigbee2mqtt",
                "server": "mqtt://localhost:1883",
                "keepalive": 60,
                "version": 4
            },
            "exclude_grouped_devices": false,
            "devices": [
                {
                    "id": "0xa4c1381c980de02e",
                    "exclude": true
                },
                {
                    "id": "0xa4c1389a3136c6d7",
                    "exclude": true
                }
            ],
            "defaults": {
                "exclude": false,
                "excluded_keys": [
                    "valve_detection",
                    "window_detection",
                    "auto_lock",
                    "away_mode"
                ],
                "values": [
                    {
                        "property": "system_mode",
                        "exclude": [
                            "heat"
                        ]
                    }
                ]
            }
        }
    ]
}
```


### Exposes information from Zigbee2MQTT

```json
{
    "auto_lock": "MANUAL",
    "away_mode": "OFF",
    "away_preset_days": 1,
    "away_preset_temperature": 15,
    "battery_low": false,
    "boost_time": 300,
    "child_lock": "UNLOCK",
    "comfort_temperature": 20,
    "current_heating_setpoint": 35,
    "eco_temperature": 15,
    "force": "close",
    "holidays": [
        {
            "hour": 6,
            "minute": 0,
            "temperature": 20
        },
        {
            "hour": 8,
            "minute": 0,
            "temperature": 15
        },
        {
            "hour": 11,
            "minute": 30,
            "temperature": 15
        },
        {
            "hour": 12,
            "minute": 30,
            "temperature": 15
        },
        {
            "hour": 17,
            "minute": 30,
            "temperature": 20
        },
        {
            "hour": 22,
            "minute": 0,
            "temperature": 15
        }
    ],
    "holidays_schedule": "06:00/20°C 08:00/15°C 11:30/15°C 12:30/15°C 17:30/20°C 22:00/15°C",
    "linkquality": 33,
    "local_temperature": 19.5,
    "local_temperature_calibration": -1,
    "max_temperature": 35,
    "min_temperature": 5,
    "position": 0,
    "preset": "manual",
    "running_state": "idle",
    "system_mode": "off",
    "update": {
        "installed_version": 87,
        "latest_version": 87,
        "state": "idle"
    },
    "week": "5+2",
    "window_detection": "OFF",
    "window_detection_params": {
        "minutes": 7,
        "temperature": 17
    },
    "window_open": false,
    "workdays": [
        {
            "hour": 6,
            "minute": 0,
            "temperature": 20
        },
        {
            "hour": 8,
            "minute": 0,
            "temperature": 15
        },
        {
            "hour": 11,
            "minute": 30,
            "temperature": 15
        },
        {
            "hour": 12,
            "minute": 30,
            "temperature": 15
        },
        {
            "hour": 17,
            "minute": 30,
            "temperature": 20
        },
        {
            "hour": 22,
            "minute": 0,
            "temperature": 15
        }
    ],
    "workdays_schedule": "06:00/20°C 08:00/15°C 11:30/15°C 12:30/15°C 17:30/20°C 22:00/15°C"
}
```


### Additional information / Other remarks

_No response_