Describe `payload.user.mfa_config` parameter

[FreddyDevelop]

The payload.user.mfa_config parameter have no description and this might confuse users what each parameter means.

Especially because the payload.user.mfa_config.totp_enabledand payload.user.mfa_config. security_keys_enabled only indicate that the tenant has enabled the config for both, but not that the user has configured them.

For TOTP you must look at auth_app_set_up to check if user has configured a TOTP app.
For security keys you must look at payload.user.security_keys to check if the user has enrolled security keys.

We should add descriptions for the parameters in payload.user.mfa_config to prevent confusion.