LFS protocol support

Expose LFS batch protocol [1] from the standard LFS URL:

  http://gerrit/path/to/project/info/lfs/*

as this is the default URL where the git-lfs client [2] expects the LFS
protocol. Therefore, no additional configuration of the git-lfs client
is required.

LFS protocol requests are forwarded to the configured lfs.plugin.
If no lfs.plugin is defined, Gerrit responds with "501 Not Implemented"
to all LFS protocol requests.

User authentication is the same as for git-over-http protocol. An
additional advantage of using the standard LFS URL is that the git-lfs
client will reuse the authentication credentials used for the
git-over-http because the schema and the host name are the same.

NOTE: Currently the standard git-lfs client only supports basic
authentication. This means that Gerrit must be configured to support
basic authentication.

[1] https://github.com/github/git-lfs/blob/master/docs/api/http-v1-batch.md
[2] https://git-lfs.github.com/

Change-Id: I1e3f29789d73af52c60d3788ee4fd2e7024b1c0c
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index ce9b1b3..2436448 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -2851,6 +2851,17 @@
   javaOptions = -Dcom.sun.jndi.ldap.connect.pool.timeout=300000
 ----
 
+[[lfs]]
+=== Section lfs
+
+[[lfs.plugin]]lfs.plugin::
++
+The name of a plugin which serves the LFS protocol on the
+`<project-name>/info/lfs/objects/batch` endpoint. When not configured Gerrit
+will respond with `501 Not Implemented` on LFS protocol requests.
++
+By default unset.
+
 [[log]]
 === Section log