Draft: Add advisory lock to LFS objects projects

What does this MR do and why?

We want to deduplicate the lfs_objects_projects table by lfs_object_id, project_id, and repository_type. To achieve this, we have !154323, which creates a batched background migration. However, we should should also avoid creating new duplicates in the lfs_objects_projects table during the deduplicate migration.

This MR introduces an explicit locking mechanism (advisory lock) in the lfs_object_project model, which is executed on every record creation (except bulk insert, which is not likely the source for duplications). This advisory lock will be taken by a new callback and affect the 3 column values if they are present. Also, this callback should be behind an FF to be sure about its effectiveness and behavior.

Context: !154323 (comment 1994629812)

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Related to #199909