Web IDE: Empty states, blocked tabs and other messages
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=390815)
</details>
<!--IssueSummary end-->
### Problem
Some features will be not available for users on the first release or because of an administrator restriction. So we need to show this information to our users.
### Proposal
Debug tab
<img src="/uploads/a7e289f07799065592397e2626224bac/Debug_-_Disabled.png" width="250" />
Extension market
| it's not available | admin blocked this tab | agreement |
| ------ | ------ | ------ |
| <img src="/uploads/cc70ee56f36f3aed891d7435ab3f3963/Extensions_-_Disabled.png" width="250" /> | <img src="/uploads/afc73e697c75f9d6dc24b5bd8b5aee0d/Extensions_-_Disabled_by_admin.png" width="250" /> | in progress |
Search
<img src="/uploads/cc5f55556dde5b6ac1019315f48ee35e/search.png" width="250" />
issue