Deprecate old LB options, fix endpoint sync. (#287)

* Depreate old LB options, fix endpoint sync.

- deprecate useLoadBalancer, replicaLoadBalancer from the manifest
  and enable_load_balancer from the operator configuration. The old
  operator configuration options become no-op with this commit. For
  the old manifest options, `useLoadBalancer` and `replicaLoadBalancer`
  are still consulted,  but only in the absense of the new ones
  (enableMasterLoadBalancer and enableReplicaLoadBalancer).

- Make sure the endpoint being created during the sync receives proper
  addresses subset. This is more critical for the replicas, as for the
  masters Patroni will normally re-create the endpoint before the
  operator.

- Avoid creating the replica endpoint, since it will be created automatically
  by the corresponding service.
- Update the README and unit tests.

Code review by @mgomezch and @zerg-junior

pkg/util/config/config.go

@@ -88,7 +88,7 @@ type Config struct {
 	EnableMasterLoadBalancer    bool   `name:"enable_master_load_balancer" default:"true"`
 	EnableReplicaLoadBalancer   bool   `name:"enable_replica_load_balancer" default:"false"`
 	// deprecated and kept for backward compatibility
-	EnableLoadBalancer       *bool             `name:"enable_load_balancer" default:"true"`
+	EnableLoadBalancer       *bool             `name:"enable_load_balancer"`
 	MasterDNSNameFormat      stringTemplate    `name:"master_dns_name_format" default:"{cluster}.{team}.{hostedzone}"`
 	ReplicaDNSNameFormat     stringTemplate    `name:"replica_dns_name_format" default:"{cluster}-repl.{team}.{hostedzone}"`
 	PDBNameFormat            stringTemplate    `name:"pdb_name_format" default:"postgres-{cluster}-pdb"`