[MM-13840] Change eMail as a post-verification action (#10253)

* Change eMail as a post-verification action

* Fix broken test

* comment for special behavior, tests

* govet

* Check for already existent eMails when require email verification is turned on before accepting update

app/email.go

@@ -180,7 +180,7 @@ func (a *App) SendWelcomeEmail(userId string, email string, verified bool, local
 	}
 
 	if !verified {
-		token, err := a.CreateVerifyEmailToken(userId)
+		token, err := a.CreateVerifyEmailToken(userId, email)
 		if err != nil {
 			return err
 		}