Replace restricted Bitnami PostgreSQL HA image in Gitea chart to ensure reliable platform deployments

Hi,

I was reviewing the App Platform components and noticed that the embedded Gitea sub-chart for PostgreSQL High Availability (`charts/gitea/charts/postgresql-ha`) relies on the `bitnami/postgresql-repmgr` Docker image.

**The Problem**
Bitnami has recently restricted public access to their Docker images, placing them behind a paywall with strict rate limits. Relying on the `bitnami/postgresql-repmgr` namespace now frequently results in `pull access denied` errors. For a core platform offering like App Platform on Linode Kubernetes Engine, these access restrictions pose a significant risk of failing automated cluster provisioning, breaking updates for users, and degrading the "out of the box" installation experience.

**Proposed Solution**
I suggest switching to **`soldevelo/postgresql-repmgr`**.
This image is a free, actively maintained, and fully open-source fork of the original Bitnami image.

Crucially, it is a **drop-in replacement**:
* It preserves the exact same environment variables used for `repmgr` clustering and failover logic.
* It maintains the same internal paths and volume mounts (e.g., `/bitnami/postgresql`).
* Your existing Helm chart values (`charts/gitea/charts/postgresql-ha/values.yaml`) and deployment scripts will continue to work immediately without requiring any refactoring.

*(Note: SolDevelo maintains a growing library of open-source, Bitnami-compatible images to help the community bypass these new restrictions. You can find the source code and other images here: [https://github.com/SolDevelo/containers](https://github.com/SolDevelo/containers))*

**Suggested Changes:**

In `charts/gitea/charts/postgresql-ha/Chart.yaml`:
```yaml
# Old
- name: postgresql-repmgr
image: docker.io/bitnami/postgresql-repmgr:17.6.0-debian-12-r2

# New
- name: postgresql-repmgr
image: docker.io/soldevelo/postgresql-repmgr:17.6.0-debian-12-r2
```

**Affected files:**
* `charts/gitea/charts/postgresql-ha/Chart.yaml`
* `charts/gitea/charts/postgresql-ha/README.md`
* `charts/gitea/README.md`

I can submit a Pull Request to update the image references across the repository to ensure App Platform setups remain reliable and accessible for all users. Would you be open to that?

Review the image references and deployment details in charts/gitea/charts/postgresql-ha/Chart.yaml and the affected README.md files. Confirm the replacement preserves the documented PostgreSQL HA configuration, paths, and volume mounts, then update all listed references so the chart documentation and deployment image are consistent.

Written by the indexing model from the issue text.