[backups] Scaffold a Velero strategy (#1742)

## What this PR does

This patch adds boilerplate code for a Velero strategy for the backups
API. Implementation can be added into the Reconcile function in a
subsequent PR.

###

```release-note
[backups] Add the boilerplate for a new Velero strategy for backups.
```

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added Velero as a supported backup strategy, including a
cluster-scoped Velero resource type and CRD for creating Velero-backed
strategies.
* Backup job controller updated to recognize and dispatch Velero-backed
jobs, with status conditions exposed for monitoring progress and health.
* Introduced basic reconciliation flow for Velero strategy to enable
future behavior and observability.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

cmd/backupstrategy-controller/main.go

@@ -147,7 +147,7 @@ func main() {
 		os.Exit(1)
 	}
 
-	if err = (&backupcontroller.BackupJobStrategyReconciler{
+	if err = (&backupcontroller.BackupJobReconciler{
 		Client: mgr.GetClient(),
 		Scheme: mgr.GetScheme(),
 	}).SetupWithManager(mgr); err != nil {