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/delete_kustomization.go

@@ -29,6 +29,7 @@ var deleteKsCmd = &cobra.Command{
 	Long:    "The delete kustomization command deletes the given Kustomization from the cluster.",
 	Example: `  # Delete a kustomization and the Kubernetes resources created by it
   flux delete kustomization podinfo`,
+	ValidArgsFunction: resourceNamesCompletionFunc(kustomizev1.GroupVersion.WithKind(kustomizev1.KustomizationKind)),
 	RunE: deleteCommand{
 		apiType: kustomizationType,
 		object:  universalAdapter{&kustomizev1.Kustomization{}},