[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

api4/user.go

@@ -1355,7 +1355,7 @@ func sendVerificationEmail(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if err = c.App.SendEmailVerification(user); err != nil {
+	if err = c.App.SendEmailVerification(user, user.Email); err != nil {
 		// Don't want to leak whether the email is valid or not
 		mlog.Error(err.Error())
 		ReturnStatusOK(w)