DEV: Refactor the api docs for the user endpoint (#14377)

Due to the way that rswag expands shared components we were getting this
warning when linting our api docs:

```
Component: "user_response" is never used.
```

This change refactors the `api/users_spec.rb` file so that it uses the
new way of doing things with a separate `user_get_response.json` schema
file rather then the old way of loading a shared response inside of the
swagger_helper.rb file.

spec/requests/api/schemas/json/user_create_response.json

@@ -0,0 +1,22 @@
+{
+  "additionalProperties": false,
+  "properties": {
+    "success": {
+      "type": "boolean"
+    },
+    "active": {
+      "type": "boolean"
+    },
+    "message": {
+      "type": "string"
+    },
+    "user_id": {
+      "type": "integer"
+    }
+  },
+  "required": [
+    "success",
+    "active",
+    "message"
+  ]
+}