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/export_helmrelease.go

@@ -33,6 +33,7 @@ var exportHelmReleaseCmd = &cobra.Command{
 
   # Export a HelmRelease
   flux export hr my-app > app-release.yaml`,
+	ValidArgsFunction: resourceNamesCompletionFunc(helmv2.GroupVersion.WithKind(helmv2.HelmReleaseKind)),
 	RunE: exportCommand{
 		object: helmReleaseAdapter{&helmv2.HelmRelease{}},
 		list:   helmReleaseListAdapter{&helmv2.HelmReleaseList{}},