Expose three options to configure queueing limits:
- apiLimit
- apiQueueLimit
- apiQueueTimeout

Suppress upload-pack Wait() error on shallow clone

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/36

It is a [known
bug](https://gitlab.com/gitlab-org/gitlab-workhorse/issues/36#note_4761298)
in git-upload-pack that it exits unsuccessfully when the client does a
'shallow clone'. We don't want this non-zero process exit status to
clutter our logs. In this change we buffer the first 4kB of the request body for
git upload-pack and scan for a 'deepen' message (which indicates the
clients wants to do a shallow clone). If deepen is found we suppress
error reporting for a non-zero exit status of git upload-pack.


See merge request !71

Improve errors

- Add request metadata (method, path)
- Sentry improvement: custom types for common errors

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/64

See merge request !69

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/63

- Add request metadata (method, path)
- Sentry improvement: custom types for common errors

Support more archive extensions in SendArchive

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/60

See merge request !66

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/60

Pass version as 'release' to Sentry



See merge request !64

Add Sentry remote error collection

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/57

Vendors:
- https://github.com/getsentry/raven-go (unnamed permissive license)
- https://github.com/certifi/gocertifi (Mozilla Public License 2.0)

Discussed licenses with @JobV; they seem OK.

See merge request !63

API safeties

Increase security and sanity checks to allow for new features.

- ability to exchange signed information with gitlab-rails via a shared secret
- content-type checks to prevent leaking internal API data

Signed messages are implemented using JWT. To make this possible we vendor the jwt-go library.

Companion MR in gitlab-rails: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5907

See merge request !60