engine: resources: Make consul optional

Licensing has made this non-free. Let's put that behind a build tag for
now, and remove it entirely if no suitable libre replacement is found.

engine/resources/consul_kv.go

@@ -27,6 +27,8 @@
 // additional permission if he deems it necessary to achieve the goals of this
 // additional permission.
 
+//go:build !noconsul
+
 package resources
 
 import (

engine/resources/consul_kv_test.go

@@ -27,7 +27,7 @@
 // additional permission if he deems it necessary to achieve the goals of this
 // additional permission.
 
-//go:build !root
+//go:build !root || !noconsul
 
 package resources