init: add an option --enable-git-lfs-filter

It was reported that git-lfs did not work with git-repo. Specifically,
`git read-tree -u` run by `repo sync` would fail git-lfs's smudge
filter. See https://github.com/github/git-lfs/issues/1422.

In fact, by the time `git read-tree -u` is run, the repository is not
bare. It is just that, the working directory is not the same as the
.git directory. git-lfs's filter should work. No one seems to have
delved into that issue.

Today, with newer versions of git-repo and git-lfs, that issue will
not reproduce. Tested with
- git 2.33, git-lfs 2.13 on macOS
- git 2.17, git-lfs 2.3 on ubuntu

So, it seems fine to add an option --enable-git-lfs-filter, default to
false, and stat that it may not work with older versions of git and
git-lfs in the help doc.

Bug: https://crbug.com/gerrit/14516
Change-Id: I8d21854eeeea541e072f63d6b10ad1253b1a9826
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/328359
Tested-by: XD Trol <milestonejxd@gmail.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

docs/internal-fs-layout.md

@@ -163,6 +163,7 @@ User controlled settings are initialized when running `repo init`.
 | repo.clonefilter         | `--clone-filter`          | Filter setting when using [partial git clones] |
 | repo.depth               | `--depth`                 | Create shallow checkouts when cloning |
 | repo.dissociate          | `--dissociate`            | Dissociate from any reference/mirrors after initial clone |
+| repo.git-lfs             | `--git-lfs`               | Enable [Git LFS] support |
 | repo.mirror              | `--mirror`                | Checkout is a repo mirror |
 | repo.partialclone        | `--partial-clone`         | Create [partial git clones] |
 | repo.partialcloneexclude | `--partial-clone-exclude` | Comma-delimited list of project names (not paths) to exclude while using [partial git clones] |
@@ -254,6 +255,7 @@ Repo will create & maintain a few files in the user's home directory.
 
 
 [git-config]: https://git-scm.com/docs/git-config
+[Git LFS]: https://git-lfs.github.com/
 [git worktree]: https://git-scm.com/docs/git-worktree
 [gitsubmodules]: https://git-scm.com/docs/gitsubmodules
 [manifest-format.md]: ./manifest-format.md