Docs(SSO): Improve Authelia Configuration

[valentimarco]

Is your feature request related to a problem? Please describe.
As first timer in SSO, i found confusing the <client-secret> used in both configs

Describe the solution you'd like
Specify with different names that:

• Authelia side: client_secret in configuration.yaml is the pbkdf2 hash of the password generated (Digest part of the image) .
• mas side: client_secret in the config is the password generated from the command above (Random Password part of the image).

Describe alternatives you've considered
Declare two names like client_secret_hash and client_secret.

Additional context
If i have time, i will provide a PR if we agree on the solution