Add warning when project with LFS files is missing .gitattributes

What does this MR do and why?

Related to #429467 (closed) we have found some projects got into a state where there were git-lfs files in the project but the project was missing the .gitattributes file. This is effectively a corrupted project as the git-lfs plugin won't know about any of these files when cloning or pushing and it could lead to a lot of confusion. We are adding a warning banner on the project page for such projects to help save time troubleshooting if a project ends up in this state.

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Related to #429467 (closed)