Let users know the error via WebUI when the application is missing .pipe.yaml file

[ono-max]

What would you like to be added: Currently, piped doesn't inform users about the error message in WebUI when the application is missing .pipe.yaml file. It just outputs logs in the terminal such as:

Wait for new commit

failed to check application: 9433b090-13bf-4cbe-bb26-53bb698dfe7f	{"cloud-provider": "kubernetes-default", "error": "failed to load deployment configuration: open /var/folders/5j/z2c9zm7124q81f_py4xmd3scp7w9j7/T/git845929451/kubernetes/ono-local-wait-approval2/.pipe.yaml: no such file or directory"}
github.com/pipe-cd/pipe/pkg/app/piped/driftdetector/kubernetes.(*detector).check
	pkg/app/piped/driftdetector/kubernetes/detector.go:168
github.com/pipe-cd/pipe/pkg/app/piped/driftdetector/kubernetes.(*detector).Run
	pkg/app/piped/driftdetector/kubernetes/detector.go:110
github.com/pipe-cd/pipe/pkg/app/piped/driftdetector.(*detector).Run.func1
	pkg/app/piped/driftdetector/detector.go:131
golang.org/x/sync/errgroup.(*Group).Go.func1
	external/org_golang_x_sync/errgroup/errgroup.go:57
failed to check application: 9433b090-13bf-4cbe-bb26-53bb698dfe7f	{"error": "deployment config file kubernetes/ono-local-wait-approval2/.pipe.yaml was not found"}
github.com/pipe-cd/pipe/pkg/app/piped/trigger.(*Trigger).checkNewCommits
	pkg/app/piped/trigger/trigger.go:235
github.com/pipe-cd/pipe/pkg/app/piped/trigger.(*Trigger).Run
	pkg/app/piped/trigger/trigger.go:157
github.com/pipe-cd/pipe/pkg/app/piped/cmd/piped.(*piped).run.func15
	pkg/app/piped/cmd/piped/piped.go:386
golang.org/x/sync/errgroup.(*Group).Go.func1
	external/org_golang_x_sync/errgroup/errgroup.go:57

Push the "Sync" button

failed to get the list of mentions	{"error": "deployment config file kubernetes/ono-local-wait-approval2/.pipe.yaml was not found"}
github.com/pipe-cd/pipe/pkg/app/piped/trigger.(*Trigger).triggerDeployment
	pkg/app/piped/trigger/deployment.go:46
github.com/pipe-cd/pipe/pkg/app/piped/trigger.(*Trigger).syncApplication
	pkg/app/piped/trigger/trigger.go:266
github.com/pipe-cd/pipe/pkg/app/piped/trigger.(*Trigger).checkNewCommands
	pkg/app/piped/trigger/trigger.go:191
github.com/pipe-cd/pipe/pkg/app/piped/trigger.(*Trigger).Run
	pkg/app/piped/trigger/trigger.go:154
github.com/pipe-cd/pipe/pkg/app/piped/cmd/piped.(*piped).run.func15
	pkg/app/piped/cmd/piped/piped.go:386
golang.org/x/sync/errgroup.(*Group).Go.func1
	external/org_golang_x_sync/errgroup/errgroup.go:57
failed to sync application	{"app-id": "9433b090-13bf-4cbe-bb26-53bb698dfe7f", "error": "deployment config file kubernetes/ono-local-wait-approval2/.pipe.yaml was not found"}
github.com/pipe-cd/pipe/pkg/app/piped/trigger.(*Trigger).checkNewCommands
	pkg/app/piped/trigger/trigger.go:193
github.com/pipe-cd/pipe/pkg/app/piped/trigger.(*Trigger).Run
	pkg/app/piped/trigger/trigger.go:154
github.com/pipe-cd/pipe/pkg/app/piped/cmd/piped.(*piped).run.func15
	pkg/app/piped/cmd/piped/piped.go:386
golang.org/x/sync/errgroup.(*Group).Go.func1
	external/org_golang_x_sync/errgroup/errgroup.go:57

Why is this needed: