Detect git lfs pointer files

These are small placeholders that are fetched from another place using git lfs. They have the same name and path as the full file.
For instance:
```
version https://git-lfs.github.com/spec/v1
oid sha256:6fd5d72fe4589f189f8ebc006442dbb529bb7ce38f8082112682524616046452
size 90405214
```
The .gitattributes file of a repo also has some config:
```
*.7z filter=lfs diff=lfs merge=lfs -text
*.bin filter=lfs diff=lfs merge=lfs -text
...
```
It is not clear how to fetch these files short of using git lfs.