AuthN: Fix signout redirect url (#87631)

* Add missing return

* Use sign out redirect url from auth config if configured

* remove option from auth.jwt that is not used

pkg/api/login.go

@@ -254,6 +254,7 @@ func (hs *HTTPServer) Logout(c *contextmodel.ReqContext) {
 	if err != nil {
 		hs.log.Error("Failed perform proper logout", "error", err)
 		c.Redirect(hs.Cfg.AppSubURL + "/login")
+		return
 	}
 
 	_, id := c.SignedInUser.GetNamespacedID()