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: ![image](/uploads/903fdb9949e2d7616f62c71ad1d03db4/image.png){width=141 height=35} vs ![image](/uploads/a246cb773ad0230aaf4890c873da444e/image.png){width=141 height=35} Originally raised in: https://gitlab.com/gitlab-org/gitlab/-/issues/569464#note_2985081098
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