Adding salt_syndic_enabled to soft params

The patch adds ability to enable/disable salt-syndic
by changing the value with soft params.

Depends-on: Id97088e0a8c449c38943b8ceaa2111647fea19fc
Change-Id: I019fc1a08ae4781a1bfd39f39acf1d695691b997
Related-PROD: PROD-20579

metadata/service/syndic/cluster.yml

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

metadata/service/syndic/single.yml

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