Add size in GitEntry

The GetTreeEntries method in commit service is used to retrieve git entries information. Currently, depending on the recursive params, git-ls-tree or git-cat-file is used.

This PR MR enables the -l param in git-ls-tree in order to extract the Entry size.

I've check in git-cat-file, but seems like the Tree object, when displayed, only report Oid, Mode and Filename So this PR enable the use of git-ls-tree for listing and git-cat-file for flatpath compute.

@huggingface, we are evaluating the use of gitaly in order to scale our git server (currently on one machine using nodegit). Currently, in order to obtain the size, we load the blog git nodegit (not efficient), with this PR, we could get size of multiple Git Entry at once.