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/resume_alert.go

@@ -29,6 +29,7 @@ var resumeAlertCmd = &cobra.Command{
 finish the apply.`,
 	Example: `  # Resume reconciliation for an existing Alert
   flux resume alert main`,
+	ValidArgsFunction: resourceNamesCompletionFunc(notificationv1.GroupVersion.WithKind(notificationv1.AlertKind)),
 	RunE: resumeCommand{
 		apiType: alertType,
 		object:  alertAdapter{&notificationv1.Alert{}},