Add missing required sections to the UI and CLI documentation

The Google documentation [states](https://cloud.google.com/marketplace/docs/partners/kubernetes-solutions/create-app-package#user-guide) that the user guide should contain certain sections. In the following list, I have checked the items that we already have:

- [x] Overview
- [x] One-time setup
- [x] Installation
- [x] Basic Usage (I added a section where I explain how to create a certificate)
- [ ] Back up and restore
- [ ] Image updates
- [ ] Scaling
- [ ] Deletion

This issue aims at reminding us to add the 4 missing sections both for the UI and the CLI instructions.

Locate the existing UI and CLI user guides and compare them with the required sections listed in the issue. Add Back up and restore, Image updates, Scaling, and Deletion to both guides; done means all four sections are present in each set of instructions.

Rédigé par le modèle d'indexation à partir du texte de l'issue.