[Docs]: Please add links to pgBackRest-based backup plugins

### Is there an existing issue already for your request/idea?

- [x] I have searched for an existing issue, and could not find anything. I believe this is a new documentation enhancement to be evaluated.

### What problem in the existing documentation this issue aims to solve?

There are few more CNPG-I base plugins in the world besides Barman Cloud

### Describe what additions need to be done to the documentation

Could you please add two CNPG-I plugins which are based on `pgbackrest` tool list in main README.md?

They are from:
- [Opera Software](https://github.com/operasoftware/cnpg-plugin-pgbackrest)
- [Dalibo](https://github.com/dalibo/cnpg-plugin-pgbackrest)

### Describe what pages need to change in the documentation, if any

Main README.md in section about available CNPG-I plugins

### Describe what pages need to be removed from the documentation, if any

_No response_

### Additional context

_No response_

### Backport?

Yes

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct