Helm: add podDisruptionBudget

**Describe the solution you'd like**
The helm chart should include an explicit podDisruptionBudget to ensure the required availability of the controller is specified.

**Anything else you would like to add:**
A PDB that says all pods can be down is still useful because it is explicit.

**Environment:**

- Secrets Store Sync Controller version: (use the image tag): 0.0.2
- Kubernetes version: (use `kubectl version`): 1.33.0

Start by locating the Helm chart and its templates, then inspect how Kubernetes resources are defined and validated. Add an explicit PodDisruptionBudget for the controller, allowing all pods to be down as requested, and render or test the chart to confirm the resource is included.

Written by the indexing model from the issue text.