Add initcontainer to wait for PostgreSQL

It was possible that Nextcloud started without PostgreSQL being ready.
This new initcontainer will make sure that PostgreSQL is reachable
before attempting to start the main Nextcloud container.

pkg/comp-functions/functions/vshnnextcloud/deploy.go

@@ -242,6 +242,7 @@ func newValues(ctx context.Context, svc *runtime.ServiceRuntime, comp *vshnv1.VS
 	}
 
 	externalDb := map[string]any{}
+	extraInitContainers := []map[string]any{}
 
 	if comp.Spec.Parameters.Service.UseExternalPostgreSQL {
 		cd, err := svc.GetObservedComposedResourceConnectionDetails(comp.GetName() + pgInstanceNameSuffix)
@@ -264,6 +265,24 @@ func newValues(ctx context.Context, svc *runtime.ServiceRuntime, comp *vshnv1.VS
 			"user":     string(cd[vshnpostgres.PostgresqlUser]),
 			"password": string(cd[vshnpostgres.PostgresqlPassword]),
 		}
+
+		extraInitContainers = []map[string]any{
+			{
+				"name":  "dbchecker",
+				"image": "docker.io/busybox",
+				"command": []string{
+					"sh",
+					"-c",
+					`echo 'Waiting for Database to become ready...'
+
+              until printf "." && nc -z -w 2 ` + string(cd[vshnpostgres.PostgresqlHost]) + " " + string(cd[vshnpostgres.PostgresqlPort]) + `; do
+                  sleep 2;
+              done;
+
+              echo 'Database OK ✓'`,
+				},
+			},
+		}
 	}
 
 	configString := svc.Config.Data["isOpenshift"]
@@ -297,8 +316,9 @@ func newValues(ctx context.Context, svc *runtime.ServiceRuntime, comp *vshnv1.VS
 			"configs": map[string]string{
 				"vshn-nextcloud.config.php": updatedNextcloudConfig,
 			},
-			"containerPort":      8080,
-			"podSecurityContext": securityContext,
+			"extraInitContainers": extraInitContainers,
+			"containerPort":       8080,
+			"podSecurityContext":  securityContext,
 			"extraVolumes": []map[string]any{
 				{
 					"name": "apache-config",