Add dynamic completion suppport

This commit adds dynamic completion support for the following commands
and flags:

- `flux delete ...` command
- `flux export ...` command
- `flux get ...` command
- `flux reconcile ...` command
- `flux resume ...` command
- `flux suspend ...` command
- `--namespace` flag
- `--context` flag

Signed-off-by: Kazuki Suda <kazuki.suda@gmail.com>

cmd/flux/suspend_receiver.go

@@ -28,6 +28,7 @@ var suspendReceiverCmd = &cobra.Command{
 	Long:  "The suspend command disables the reconciliation of a Receiver resource.",
 	Example: `  # Suspend reconciliation for an existing Receiver
   flux suspend receiver main`,
+	ValidArgsFunction: resourceNamesCompletionFunc(notificationv1.GroupVersion.WithKind(notificationv1.ReceiverKind)),
 	RunE: suspendCommand{
 		apiType: receiverType,
 		object:  &receiverAdapter{&notificationv1.Receiver{}},