plan: Fix plan manipulating desired

Anywhere the plan is manipulating endpoints needs to work with a copy to
ensure that it doesn't change the passed in spec value. Was causing an
issue where the status was being updated incorrectly due to the
dnsrecord spec endpoints changing.

internal/external-dns/plan/plan.go

@@ -437,13 +437,14 @@ func (e *managedRecordSetChanges) calculateDesired(update *endpointUpdate) {
 	}
 
 	currentCopy := update.current.DeepCopy()
+	desiredCopy := update.desired.DeepCopy()
 
 	// A Records can be merged, but we remove the known previous target values first in order to ensure potentially stale values are removed
 	if update.current.RecordType == endpoint.RecordTypeA {
 		if update.previous != nil {
 			removeEndpointTargets(update.previous.Targets, currentCopy)
 		}
-		mergeEndpointTargets(update.desired, currentCopy)
+		mergeEndpointTargets(desiredCopy, currentCopy)
 	}
 
 	// CNAME records can be merged, it's expected that the provider implementation understands that a CNAME might have
@@ -452,16 +453,14 @@ func (e *managedRecordSetChanges) calculateDesired(update *endpointUpdate) {
 		if update.previous != nil {
 			removeEndpointTargets(update.previous.Targets, currentCopy)
 		}
-		mergeEndpointTargets(update.desired, currentCopy)
+		mergeEndpointTargets(desiredCopy, currentCopy)
 
 		//ToDo manirn Check this is actually needed, and if it is add a test that requires it to be here
-		if len(update.desired.Targets) <= 1 {
+		if len(desiredCopy.Targets) <= 1 {
 			log.Debugf("skipping check for managed dnsNames for CNAME with single target value")
 			return
 		}
 
-		desiredCopy := update.desired.DeepCopy()
-
 		// Calculate if any of the new desired targets are also managed dnsNames within this record set.
 		// If a target is not managed, do nothing and continue with the current targets.
 		// If a target is managed:
@@ -476,7 +475,7 @@ func (e *managedRecordSetChanges) calculateDesired(update *endpointUpdate) {
 
 				// If the target has no owners we can just remove it
 				if len(tOwners) == 0 {
-					removeEndpointTarget(t, update.desired)
+					removeEndpointTarget(t, desiredCopy)
 					break
 				}
 
@@ -490,13 +489,14 @@ func (e *managedRecordSetChanges) calculateDesired(update *endpointUpdate) {
 						}
 					}
 					if !hasMutualOwner {
-						removeEndpointTarget(t, update.desired)
+						removeEndpointTarget(t, desiredCopy)
 					}
 				}
 
 			}
 		}
 	}
+	update.desired = desiredCopy
 }
 
 func removeEndpointTarget(target string, endpoint *endpoint.Endpoint) {