Use gitaly-upload-pack and gitaly-receive-pack

Closes gitaly#193

See merge request !129

Handle GL_REPOSITORY env variable and use it in api calls

See merge request !130

Use a shorter socket path during testing

See merge request !131

Use recursive lookup for git repositories in the bin/create-hooks script

Closes #82

See merge request !128

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Add hello-world Go executable and gitaly-proto 0.5.0

Closes gitaly#186

See merge request !127

Explain how to release a new version

See merge request !126

adds timeout option to push branches and respective test suite

See merge request !124

Fetch repositories with --quiet option by default

See merge request !125

This will allow us to prevent deadlocks when dealing with extremely
long outputs from `git fetch`. All the pipes (stdin, stdout, and
stderr) have limited buffers, and when one fills up, everything is
going to stop.

Remove git annex support

See merge request !122

Add gitaly notification on post-receive hook

See merge request !119

Set a 'Host' header on unix sockets

Closes #72

See merge request !117

Workaround for a bug in the HTTPUNIX client.

Pass relevant git environment variables while calling `/allowed`

1. Starting version 2.11, git changed the way the pre-receive flow works.
  - Previously, the new potential objects would be added to the main repo. If the pre-receive passes, the new objects stay in the repo but are linked up. If the pre-receive fails, the new objects stay orphaned in the repo, and are cleaned up during the next `git gc`.
  - In 2.11, the new potential objects are added to a temporary "alternate object directory", that git creates for this purpose. If the pre-receive passes, the objects from the alternate object directory are migrated to the main repo. If the pre-receive fails the alternate object directory is simply deleted.
2. In our workflow, the pre-recieve script calls the `/allowed` endpoint on the
   rails server. This `/allowed` endpoint calls out directly to git to perform
   various checks. These direct calls to git do _not_ have the necessary
   environment variables set which allow access to the "alternate object
   directory" (explained above). Therefore these calls to git are not able to
   access any of the new potential objects to be added during this push.

3. We fix this by passing the relevant environment variables
   (`GIT_ALTERNATE_OBJECT_DIRECTORIES`, `GIT_OBJECT_DIRECTORY`, and
   `GIT_QUARANTINE_PATH`) to the `/allowed` endpoint, which will then include
   these environment variables while calling out to git.

---

- Related to gitlab-org/gitlab-ce#25301. 
- Corresponding backend MR: gitlab-org/gitlab-ce!7967
- Corresponding EE MR: gitlab-org/gitlab-ee!964

See merge request !112