Deployment fails with postgresql.enabled=true due to Bitnami image deprecation

### Official Helm Chart version

1.10.0

### Apache Airflow version

2.9.3

### Kubernetes Version

1.26.4

### What happened

I’d like to report an issue we encountered when deploying Airflow 2.9.3 with the Helm chart.
(This is my first issue report, so please let me know if I need to provide additional information! 🤣)

#### Environment
- Airflow version: 2.9.3
- Helm chart version: 1.1.0

#### Problem
When using the default setting postgresql.enabled: true, the chart pulls the Bitnami PostgreSQL image. Recently Bitnami (VMware) restricted access and moved many images to legacy, which leads to:

ErrImagePull / ImagePullBackOff during deployment or rollout if the legacy registry is not explicitly configured

Using images without ongoing security updates (legacy only)

In our case, the deployment failed until we manually reconfigured the chart to point at the legacy Bitnami registry. This workaround resolves the immediate deployment issue but is not sustainable, since legacy images will no longer receive security patches and may eventually become unavailable.

### How to reproduce

1. Set the value postgresql.enabled: true in values.yaml.
2. Deploy the Helm chart.
3. Observe that the deployment fails with ErrImagePull / ImagePullBackOff due to the Bitnami PostgreSQL image being pulled from the legacy registry.

### Are you willing to submit PR?

- [x] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Start with the Helm chart values for postgresql.enabled and the PostgreSQL image and registry settings. Reproduce the deployment on Kubernetes 1.26.4 with chart version 1.1.0, then verify that the default configuration no longer causes ErrImagePull or ImagePullBackOff and uses an image source with ongoing security updates.

Written by the indexing model from the issue text.