Linux Fix Vault Documentation

[DaintyJet]

Fix the documentation to have correct file endings, and be organized (How do all those files fit together and what do they mean).

[DaintyJet]

Migrate the Vault docs in the Linux folder to the Secrets Management folder when fixing them.

https://github.com/UML-Cyber-Security/CCDC_Practice_Infrastructure/tree/main/OperatingSystem-Services/Service-Secret_Management