Orchagent changes needed to support single ASIC VOQ Fixed-System (sonic-net#3847)

What I did

Portorch, Neighorch, Intfsorch are updated to not access chassis app DB. Chassis app DB is accessed only if the chassisdb.conf is present indicating its a real chassis (not a FS VOQ)
For lag creation, system lags are created as the switch is a VOQ swtich.
Why I did it

For a fixed system, there is no chassis DB present
How I verified it

Ran sonic-mgmt tests to verify BGP, LAG, functionality

Author: lakshmi-nexthop

tests/conftest.py

@@ -1704,6 +1704,11 @@ def create_vct_ctn(self, ctndir):
             vol = {}
             vol[chassis_config_dir] = {"bind": "/usr/share/sonic/virtual_chassis", "mode": "ro"}
 
+            # Mount database_config.json when connect_to_chassis_db is set to 1
+            if defcfg.get("connect_to_chassis_db") == 1:
+                database_config_file = cwd + "/virtual_chassis/database_config.json"
+                vol[database_config_file] = {"bind": "/etc/sonic/database_config.json", "mode": "ro"}
+
             # pass self.ns into the vs to be use for vs restarts by swss conftest.
             # connection to chassbr is setup by chassis_connect.py within the vs
             data = {}

tests/virtual_chassis/database_config.json

@@ -0,0 +1,97 @@
+{
+    "INSTANCES": {
+        "redis":{
+            "hostname" : "127.0.0.1",
+            "port" : 6379,
+            "unix_socket_path" : "/var/run/redis/redis.sock"
+        },
+        "redis_chassis":{
+            "hostname" : "10.8.1.200",
+            "port" : 6380,
+            "unix_socket_path" : "/var/run/redis/redis_chassis.sock"
+        }
+    },
+    "DATABASES" : {
+        "APPL_DB" : {
+            "id" : 0,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "ASIC_DB" : {
+            "id" : 1,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "COUNTERS_DB" : {
+            "id" : 2,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "CONFIG_DB" : {
+            "id" : 4,
+            "separator": "|",
+            "instance" : "redis"
+        },
+        "PFC_WD_DB" : {
+            "id" : 5,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "FLEX_COUNTER_DB" : {
+            "id" : 5,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "STATE_DB" : {
+            "id" : 6,
+            "separator": "|",
+            "instance" : "redis"
+        },
+        "SNMP_OVERLAY_DB" : {
+            "id" : 7,
+            "separator": "|",
+            "instance" : "redis"
+        },
+        "GB_ASIC_DB" : {
+            "id" : 9,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "GB_COUNTERS_DB" : {
+            "id" : 10,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "GB_FLEX_COUNTER_DB" : {
+            "id" : 11,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "CHASSIS_APP_DB" : {
+            "id" : 12,
+            "separator": "|",
+            "instance" : "redis_chassis"
+        },
+        "APPL_STATE_DB" : {
+            "id" : 14,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "DPU_APPL_DB" : {
+            "id" : 15,
+            "separator": ":",
+            "instance" : "redis"
+        },
+        "DPU_APPL_STATE_DB" : {
+            "id" : 16,
+            "separator": "|",
+            "instance" : "redis"
+        },
+        "DPU_STATE_DB": {
+            "id": 17,
+            "separator": "|",
+            "instance": "redis"
+        }
+    },
+    "VERSION" : "1.0"
+}