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.

api/jobs_test.go

@@ -576,7 +576,7 @@ func TestJobs_Canonicalize(t *testing.T) {
 								Name:   "redis",
 								Driver: "docker",
 								Config: map[string]interface{}{
-									"image": "redis:3.2",
+									"image": "redis:7",
 									"port_map": []map[string]int{{
 										"db": 6379,
 									}},
@@ -708,7 +708,7 @@ func TestJobs_Canonicalize(t *testing.T) {
 								Name:   "redis",
 								Driver: "docker",
 								Config: map[string]interface{}{
-									"image": "redis:3.2",
+									"image": "redis:7",
 									"port_map": []map[string]int{{
 										"db": 6379,
 									}},