Implement changing working folder in RD WebIDE
## Problem
When accessing Workspace through WebIDE, it's currently impossible to change the working folder in VS Code.
| WebIDE | WebUI (built-in to the server) |
| ------ | ------ |
|  |  |
This is caused by the WebIDE sandboxing the VS Code UI in an `iframe`. By default VS Code tries to change the URL in the `window.location` to reflect the new folder. This can't be done from the `iframe`.
## Proposed solution
Implement a mechanism that doesn't rely on `window.location` (URL) to change VS Code working folder path.
## More details
- This issue has been first discovered here https://gitlab.com/gitlab-org/gitlab/-/issues/368980#note_1070204630
- Paul suggested a solution in this comment: https://gitlab.com/gitlab-org/gitlab/-/issues/368980#note_1042375777
- I use the term `working folder` for VS Code workspace folder, trying to avoid the confusion with our term `Workspace`
issue