Add Git LFS support

[remilapeyre]

Closes #869

[remilapeyre]

@lkysow I made some tests and this seems to work, I've some trouble to write a unit test for it though as Git LFS expect having an HTTP server to read the file from and does not support the file:// protocol yet.

[codecov]

Codecov Report

Merging #872 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #872   +/-   ##
=======================================
  Coverage   71.87%   71.87%           
=======================================
  Files          65       65           
  Lines        5244     5244           
=======================================
  Hits         3769     3769           
  Misses       1188     1188           
  Partials      287      287

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[lkysow]

I just tested a git lfs repo on an Atlantis Docker image where git-lfs is installed and git lfs install was run and everything works fine. Why do we need the additional git lfs pull command?

[remilapeyre]

Just checked and it seems that recent packages install git-lfs in the global Git configuration so it should work without manually pulling indeed. I'm not sure why the documentation at https://github.com/git-lfs/git-lfs/wiki/Installation says that git lfs install must be run, it seems unnecessary. Do you want me to revert the changes on server/events/working_dir.go?

[lkysow]

Do you want me to revert the changes on server/events/working_dir.go?

Yes please.

Also test that git lfs install isn't necessary. If it is, it needs to be run on the Docker image.

[remilapeyre]

Also test that git lfs install isn't necessary

I tried on alpine, Debian and Centos and it seems to run on install now. It seems to be like this for Debian since 2016 (https://github.com/git-lfs/git-lfs/blob/master/debian/postinst).

[Charg]

Thanks for creating the PR @remilapeyre. Do we require any additional testing? My environment depends on LFS making this a really nice addition to Atlantis for us.

[rguevara84]

This Is great, we depend on this change too, would be nice to get it merged 💯

[lkysow]

Sorry for the delay here.