🐛 awsmachine: only register machine to LB when it's running

The AWS docs [1] state that to register an instance with the Load
Balancer target groups, the instance must be running. Currently, CAPA
tries to register it while it's still pending, causing the following
error:

```
0314 22:24:18.512176  701419 awsmachine_controller.go:605] "failed to reconcile LB attachment" err=<
    [could not register machine to load balancer: could not register control plane instance "i-039bb22b1e8df7c99" with load balancer: failed to register instance with target group 'mrb-capa-67-d2pfx-int-22623': InvalidTarget: The following targets are not in a running state and cannot be registered: 'i-039bb22b1e8df7c99'
        status code: 400, request id: 17514354-77ac-42b1-a882-489760563bbd, could not register machine to load balancer: could not register control plane instance "i-039bb22b1e8df7c99" with load balancer: failed to register instance with target group 'mrb-capa-67-d2pfx-ext-6443': InvalidTarget: The following targets are not in a running state and cannot be registered: 'i-039bb22b1e8df7c99'
        status code: 400, request id: 84e1849c-abb7-4af9-9220-8791fdc1a3fb]
 >
I0314 22:24:18.512325  701419 recorder.go:104] "events: Failed to register control plane instance \"i-039bb22b1e8df7c99\" with load balancer: failed to register instance with target group 'mrb-capa-67-d2pfx-ext-6443': InvalidTarget: The following targets are not in a running state and cannot be registered: 'i-039bb22b1e8df7c99'\n\tstatus code: 400, request id: 84e1849c-abb7-4af9-9220-8791fdc1a3fb" type="Warning" object={"kind":"AWSMachine","namespace":"openshift-cluster-api-guests","name":"mrb-capa-67-d2pfx-bootstrap","uid":"58af1162-380b-4f3e-93fe-c0e81401070e","apiVersion":"infrastructure.cluster.x-k8s.io/v1beta2","resourceVersion":"562"} reason="FailedAttachControlPlaneELB"
```

Even though this doesn't stop the install from succeeding, let's wait
for the instance state to be "running" and with that avoid unnecessary
AWS API calls.

[1] https://docs.aws.amazon.com/elasticloadbalancing/latest/application/target-group-register-targets.html#register-instances

controllers/awsmachine_controller.go

@@ -945,6 +945,15 @@ func (r *AWSMachineReconciler) reconcileLBAttachment(machineScope *scope.Machine
 			continue
 		}
 
+		// See https://docs.aws.amazon.com/elasticloadbalancing/latest/application/target-group-register-targets.html#register-instances
+		if ptr.Deref(machineScope.GetInstanceState(), infrav1.InstanceStatePending) != infrav1.InstanceStateRunning {
+			const msg = "instance is not running"
+			r.Recorder.Eventf(machineScope.AWSMachine, corev1.EventTypeWarning, "FailedAttachControlPlaneELB",
+				"Cannot register control plane instance %q with load balancer: %s", i.ID, msg)
+			conditions.MarkFalse(machineScope.AWSMachine, infrav1.ELBAttachedCondition, infrav1.ELBAttachFailedReason, clusterv1.ConditionSeverityInfo, msg)
+			continue
+		}
+
 		if err := r.registerInstanceToLBs(machineScope, elbsvc, i, lbSpec); err != nil {
 			errs = append(errs, errors.Wrapf(err, "could not register machine to load balancer"))
 		}