Adding metadata for syndic master functionality

The patch addes new metadata to configure syndic master. The master.yml
will consits of all relevant parameters required for syndic master of
masters configuration.

Change-Id: I75c274dda7ea7a388cfd5c0b3fa50e110f57a241
Related-PROD: PROD-16861

metadata/service/master/syndic.yml

+parameters:
+  salt:
+    master:
+      order_masters: true

metadata/service/syndic/cluster.yml

+parameters:
+  salt:
+    syndic:
+      enabled: true
+      masters:
+      - host: ${_param:salt_syndic_master_address_01}
+      - host: ${_param:salt_syndic_master_address_02}

metadata/service/syndic/single.yml

+parameters:
+  salt:
+    syndic:
+      enabled: true
+      master:
+        host: ${_param:salt_syndic_master_address}