cli: update default redis and use nomad service discovery

Closes #12927
Closes #12958

This PR updates the version of redis used in our examples from 3.2 to 7.
The old version is very not supported anymore, and we should be setting
a good example by using a supported version.

The long-form example job is now fixed so that the service stanza uses
nomad as the service discovery provider, and so now the job runs without
a requirement of having Consul running and configured.

scripts/example_weave.bash

@@ -42,7 +42,7 @@ job "weave-example" {
     task "redis" {
       driver = "docker"
       config {
-        image = "redis:3.2"
+        image = "redis:7"
         port_map {
           db = 6379
         }