[Banner] Added BANNER_MESSAGE table to ConfigDB (#826)

- Why I did it
Added Banner feature related Config DB table according to HLD: sonic-net/SONiC#1361

- How I did it
Added Banner table name to schema.h.

Signed-off-by: Yevhen Fastiuk <yfastiuk@nvidia.com>

common/schema.h

@@ -440,6 +440,7 @@ namespace swss {
 #define CFG_CHASSIS_MODULE_TABLE                    "CHASSIS_MODULE"
 
 #define CFG_TWAMP_SESSION_TABLE_NAME                "TWAMP_SESSION"
+#define CFG_BANNER_MESSAGE_TABLE_NAME               "BANNER_MESSAGE"
 
 #define CFG_DHCP_TABLE                              "DHCP_RELAY"