EE: PLT-4512 Show secret in addition to QR code when activating MFA (#4427)

* EE: Update MFA to display secret for manual entry

* Width adjustments for secret (#4423)

* Add unit test

einterfaces/mfa.go

@@ -8,7 +8,7 @@ import (
 )
 
 type MfaInterface interface {
-	GenerateQrCode(user *model.User) ([]byte, *model.AppError)
+	GenerateSecret(user *model.User) (string, []byte, *model.AppError)
 	Activate(user *model.User, token string) *model.AppError
 	Deactivate(userId string) *model.AppError
 	ValidateToken(secret, token string) (bool, *model.AppError)