[Mellanox][Smartswitch] Enable CHASSIS_DB (#20533)

- Why I did it
CHASSIS_DB is required for smartswitch platforms for communication between DPU and switch about DPU health and state information. Hence we need to enable it on the smartsiwtch

- How I did it
By adding chassis_db.conf in the platform folder, The configuration in thsi file enables chassis_db

- How to verify it
Check if it the database-chassis docker is running or not

device/mellanox/x86_64-nvidia_sn4280-r0/chassisdb.conf

@@ -0,0 +1,2 @@
+start_chassis_db=1
+chassis_db_address=169.254.200.254