Add vitest tests to Gitpod (#21449)

The vitest PR is merged, we can now add vitest to Gitpod's testing pane
* #21444

We couldn't use jest in the same manner because we had to customize
`NODE_OPTIONS`.

Screenshot (look at all the cool stuff circled in red):

![image](https://user-images.githubusercontent.com/20454870/195728971-9a2eaa80-8d91-4e4f-899b-a068edb9ff30.png)

Signed-off-by: Yarden Shoham <hrsi88@gmail.com>

.gitpod.yml

@@ -31,6 +31,7 @@ vscode:
     - DavidAnson.vscode-markdownlint
     - johnsoncodehk.volar
     - ms-azuretools.vscode-docker
+    - zixuanchen.vitest-explorer
 
 ports:
   - name: Gitea