[Dual-ToR] do not allow to start mux container if Dual-ToR was not configured (#24024)

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#### Why I did it
Need to improve logic where the system decides to start Dual-ToR or not

##### Work item tracking
- Microsoft ADO **(number only)**:

#### How I did it
In [mux.service.j2](https://github.com/sonic-net/sonic-buildimage/blob/master/files/build_templates/mux.service.j2) we have a few scripts that are executed before starting the mux container (ExecStartPre):
```
[Service]
TimeoutStartSec=180
User={{ sonicadmin_user }}
ExecStartPre=/usr/local/bin/write_standby.py
ExecStartPre=/usr/local/bin/mark_dhcp_packet.py
ExecStartPre=/usr/bin/{{docker_container_name}}.sh start
ExecStart=/usr/bin/{{docker_container_name}}.sh wait
```

If any of ExecStartPre scripts have a non-zero exit code mux.sh will not start.
But currently, we always return 0.
The suggestion is to exit with code 1 when the system is not configured with Dual-ToR sybtype in DEVICE_METADATA [write_standby.py#L85 ](https://github.com/sonic-net/sonic-buildimage/blob/master/files/scripts/write_standby.py#L85).

#### How to verify it

1. Config switch with Dual-ToR config
2. make sure mux docker up and running
3. remove "subtype": "DualToR" from DEVICE_METADATA
4. config reload -y

===> mux docker is down

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Author: mssonicbld

files/scripts/write_standby.py

@@ -2,6 +2,7 @@
 
 import argparse
 import time
+import sys
 
 from sonic_py_common import logger as log
 from swsscommon.swsscommon import ConfigDBConnector, DBConnector, FieldValuePairs, ProducerStateTable, SonicV2Connector, Table
@@ -160,8 +161,8 @@ def apply_mux_config(self):
         Writes standby mux state to APP DB for all mux interfaces
         """
         if not self.is_dualtor:
-            # If not running on a dual ToR system, take no action
-            return
+            logger.log_warning("It is not a Dual-ToR system, do not start mux container")
+            sys.exit(1)
 
         if self.is_warmrestart and self.is_shutdwon:
             # If in warmrestart context, take no action