Add Settings UI enum to json schema (#10489)

Noticed the json schema was listing the option as invalid even though it's accepted by WT. So added it to schema to remove the error.

## PR Checklist
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [x] Schema updated.

## Validation Steps Performed
No longer shows as invalid in VSCode.

doc/cascadia/profiles.schema.json

@@ -546,12 +546,14 @@
             "action": { "type": "string", "pattern": "openSettings" },
             "target": {
               "type": "string",
-              "default": "settingsFile",
-              "description": "The settings file to open.",
+              "default": "settingsUI",
+              "description": "Opens Settings UI or settings file.",
               "enum": [
                 "settingsFile",
                 "defaultsFile",
-                "allFiles"
+                "allFiles",
+                "settingsUI"
+                
               ]
             }
           }