Refresh `cnpg-i-hello-world` to align with the current state of CNPG-I

The `cnpg-i-hello-world` project was created to help developers get started with building plugins for CloudNativePG using the [CNPG-I framework](https://github.com/cloudnative-pg/cnpg-i).

However, the project is now outdated and requires significant maintenance and updates to reflect the current capabilities of CNPG-I. The goal is to bring it in line with the latest state of the interface and ensure it serves as a solid reference for:

- Understanding how to use CNPG-I
- Developing and prototyping new plugins

## Tasks:

- [ ] Review and update the codebase to match the latest CNPG-I interface and conventions
- [ ] Ensure it follows the latest best practices for plugin development
- [ ] Expand and improve examples as needed
- [ ] Integrate CNPG-I documentation where appropriate to provide better guidance for developers

This issue also involves coordinating with updates to the core CNPG-I documentation to ensure consistency and discoverability.

Start by reviewing the cnpg-i-hello-world codebase against the current CNPG-I interface and conventions in the linked CNPG-I project. Audit the existing examples and documentation, then coordinate with the core CNPG-I documentation. Done means the template reflects current plugin-development practices and provides consistent, discoverable guidance.

Written by the indexing model from the issue text.