website: Add consul_key_prefix link to Consul provider navbar

This file was missed when committing the doc changes for hashicorp#5988.

Author: apparentlymart

website/source/layouts/consul.erb

@@ -16,6 +16,9 @@
                     <li<%= sidebar_current("docs-consul-resource-keys") %>>
 					<a href="/docs/providers/consul/r/keys.html">consul_keys</a>
 					</li>
+                    <li<%= sidebar_current("docs-consul-resource-key-prefix") %>>
+					<a href="/docs/providers/consul/r/key_prefix.html">consul_key_prefix</a>
+					</li>
 				</ul>
 				</li>
 			</ul>