Implement per-cluster maintenance window for Postgres automatic upgrade (#2710)

* implement maintenance window for major version upgrade 
* e2e test: fix major version upgrade test and extend with the time window
* unit test: add iteration to test isInMaintenanceWindow
* UI: show the window and enable edit via UI

pkg/cluster/majorversionupgrade.go

@@ -74,6 +74,11 @@ func (c *Cluster) majorVersionUpgrade() error {
 		return nil
 	}
 
+	if !c.isInMainternanceWindow() {
+		c.logger.Infof("skipping major version upgrade, not in maintenance window")
+		return nil
+	}
+
 	pods, err := c.listPods()
 	if err != nil {
 		return err