cloner: lfs support

[sgaist]

The current implementation of the cloner does not handle lfs content which means that people will get incomplete clones if the repository has such content and they will need to call git lfs pull manually.

Note that go git does not implement yet lfs support at all.

See the compatibility grid.

[leafty]

In the past, there had been many times when sessions would not start because lfs would use too much disk storage on clone (usually around 2x the current LFS data).

The minimum is to make LFS support opt-in (to make sure most sessions can start), and if possible provide disk size error messages to the user.

[sgaist]

@leafty these are good points.

Do you think we should also consider an option for shallow cloning ?

[leafty]

I think having a fetch depth option is most likely a low priority at the moment since cases where a git reflog reaches ~1GB or above are quite uncommon.