[NEW] Guess a user's name from SAML credentials (#15240)
[NEW] Guess a user's name from SAML credentials (#15240)

* Determine a user's name from SAML username

* Determine name only if username exists
Sing-Li/Rocket.Chat,subesokun/Rocket.Chat,subesokun/Rocket.Chat,Sing-Li/Rocket.Chat,Sing-Li/Rocket.Chat,VoiSmart/Rocket.Chat,VoiSmart/Rocket.Chat,Sing-Li/Rocket.Chat,VoiSmart/Rocket.Chat,subesokun/Rocket.Chat,subesokun/Rocket.Chat