Do not show LFS object when LFS is disabled

What does this MR do?

Prevents that a 404 is shown, when trying to download a LFS file (inside the project file browser) not managed by GitLab (instead by a custom LFS server). If lfs_enabled is set to false in the config file, the lfs pointer file is directly shown as text.

Why was this MR needed?

To support more flexibility. Git-LFS should not only be bound to the GitLab LFS Server, but it should also be possible to use alternative implementations, especially for connecting to a custom cloud storage (which is not already supported by GitLab natively), because this is a big benefit when using Git-LFS (that large files can be stored outside in "cheaper" storages).

Screenshots

Before: After:

Does this MR meet the acceptance criteria?

• Changelog entry added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #28817 (closed)