docs(step-by-step): updated Vault tutorial

[kellian-cottart]

Documentation: Step-by-step 5: Vault

Description

• Added the Keycloak compatibility step for Vault for it to work
• Changed the order of execution of commands that was hindering the process of connecting to Onyxia
• Added sparse explanations of what is being done to Vault

[garronej]

Nice!
Thank you very much for your contribution!

Just so you know, the doc is being migrated here: https://docs.onyxia.sh Markdown: https://github.com/InseeFrLab/docs.onyxia.sh

Dont need to report what you have done to the new doc, I'll do it.

Best