BUG/MAJOR: do not delete backends that were also upserted in the same cycle

When processBackendsDeletedInCycle ran, it would delete a backend even if
another route had upserted it in the same reconciliation cycle. This caused
backends shared between routes to be removed when one of the routes was
updated, breaking traffic to the remaining routes.

Fix by skipping deletion when the backend also appears in the Upserted map.

Author: hdurand0710

k8s/gate/haproxy/backends.go

@@ -1007,6 +1007,10 @@ func (b *HaproxyConfMgrImpl) processBackendsDeletedInCycle() utils.Errors {
 	var errs utils.Errors
 
 	for backendName := range b.backendsImpactedInCycle.Deleted {
+		if _, alsoUpserted := b.backendsImpactedInCycle.Upserted[backendName]; alsoUpserted {
+			// Another route upserted this backend in the same cycle: keep it.
+			continue
+		}
 		if err := b.configuration.deleteBackend(b.logger, backendName); err != nil {
 			errs.Add(err)
 			continue