Improve E2E tests to verify workspace setup via VS Code Terminal
MR: Pending
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## Description
NOTE: This is a followup from [this comment](https://gitlab.com/gitlab-org/gitlab-web-ide/-/issues/6#note_2372260527) on https://gitlab.com/gitlab-org/gitlab-web-ide/-/issues/6+s.
The Workspaces E2E/QA specs do not actually test any behavior from within the workspace.
Building on work done for the Web IDE integration testing in https://gitlab.com/gitlab-org/gitlab-web-ide/-/issues/6+s and other issues, we could leverage this for workspaces too.
E.g., opening the terminal in VS Code, and asserting on things specified in the devfile, like filesystem mounts, postStart scripts, file/env secret settings, etc.
## Acceptance criteria
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- [ ] [Describe what must be achieved to complete this issue.]
- [ ] [If applicable, please provide design specifications for this feature/enhancement.]
- [ ] [If applicable, please list any technical requirements (performance, security, database, etc.)]
## Implementation plan
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[Provide a high-level plan for implementation of this issue, including relevant technical and/or design details.]
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