Add file icons for OpenTofu `.tofu` files
<!--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>
- [Label this issue](https://contributors.gitlab.com/manage-issue?action=label&projectId=278964&issueIid=585067)
</details>
<!--IssueSummary end-->
### Proposal
Files with the `.tofu` extension (OpenTofu files) have the default/generic file icon instead of the branded OpenTofu icon. To improve the UX and achieve parity with `.tf` files, the proper icon should be added.
The official design files can be found here: https://github.com/opentofu/brand-artifacts
On the current v18.7.0:
{width=141 height=35} vs {width=141 height=35}
Originally raised in: https://gitlab.com/gitlab-org/gitlab/-/issues/569464#note_2985081098
issue