[sql] Surface exception message on login failure

Note: we don't display still the json response which might have more info.

desktop/core/src/desktop/js/apps/editor/components/sqlScratchpad/SqlScratchpad.vue

@@ -177,7 +177,7 @@
               password.value
             );
           } catch (err) {
-            errorMessage.value = 'Login failed!';
+            errorMessage.value = 'Login failed: ' + err;
             console.error(err);
             return;
           }