feat: support "Use Email as username" in org (#3002)

Signed-off-by: Grégoire Bélorgey <gregoire@jianda.fr>

controllers/account.go

@@ -169,7 +169,11 @@ func (c *ApiController) Signup() {
 
 	username := authForm.Username
 	if !application.IsSignupItemVisible("Username") {
-		username = id
+		if organization.UseEmailAsUsername && application.IsSignupItemVisible("Email") {
+			username = authForm.Email
+		} else {
+			username = id
+		}
 	}
 
 	initScore, err := organization.GetInitScore()