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/reconcile_helmrelease.go

@@ -35,6 +35,7 @@ The reconcile kustomization command triggers a reconciliation of a HelmRelease r
 
   # Trigger a reconciliation of the HelmRelease's source and apply changes
   flux reconcile hr podinfo --with-source`,
+	ValidArgsFunction: resourceNamesCompletionFunc(helmv2.GroupVersion.WithKind(helmv2.HelmReleaseKind)),
 	RunE: reconcileWithSourceCommand{
 		apiType: helmReleaseType,
 		object:  helmReleaseAdapter{&helmv2.HelmRelease{}},