Remove mistaken support for `gitlab-shell user-123`

Closes #151

See merge request gitlab-org/gitlab-shell!247

Feature flag for go/ruby gitlab-shell implementations

Closes #74

See merge request gitlab-org/gitlab-shell!233

Since the Go code now wraps the Ruby script, this makes sense and tests
the interaction of the two codebases. Over time, the number of Ruby
tests to run will approach 0.

Display helpful feedback when proxying an SSH git push to secondary request  (v2)

See merge request gitlab-org/gitlab-shell!246

Merge 8-3-stable branch changes into master

Closes #155

See merge request gitlab-org/gitlab-shell!245

Display helpful feedback when proxying an SSH git push to secondary request

See merge request gitlab-org/gitlab-shell!244

This also cleans up the output from the tests as previously, Base64 encoded output was printed.

Release GitLab Shell v8.3.2

See merge request gitlab-org/gitlab-shell!243

Fix newlines not appearing between new log entries

Closes gitlab-com/gl-infra/infrastructure#5017

See merge request gitlab-org/gitlab-shell!242

In https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5017, we
observed that lots of log messages were being dropped by Fluentd due to
missing newlines.

This occurs because there is a bug in Ruby where IO#puts calls write() twice:
once to write the main text, and another to write the newline
(https://bugs.ruby-lang.org/issues/14042). In a highly concurrent environment
like GitLab.com, this can lead to interleaved newlines.

A workaround is to use `IO#print` and append the newline ourselves.

Closes https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5017

Merge branch '154-ensure-http-status-codes-are-integers-add-missing-specs-for-various-handled-http-status-code' into 'master'

Ensure text/plain & text/html content typs are handled and add missing specs for handled HTTP status codes

Closes #154

See merge request gitlab-org/gitlab-shell!239

Ensure text/plain & text/html content typs are handled and add missing specs for handled HTTP status codes

Release 8.3.1 to fix version numbering

See merge request gitlab-org/gitlab-shell!241

Release v8.3.0

See merge request gitlab-org/gitlab-shell!240

Includes custom action support for proxying SSH to a Geo secondary

Custom Action support

See merge request gitlab-org/gitlab-shell!215

Release gitlab-shell v8.2.1

See merge request gitlab-org/gitlab-shell!238

GitlabConfig spec was relying upon real config.yml

Proper HTTP status code support for /api/v4/allowed API endpoint

Closes gitlab-ce#51211

See merge request gitlab-org/gitlab-shell!237

* Previously, a 200 (OK) was sent when the user was unauthorised or the project was not found (or the user didn't have access)
* We still treat 401 and 404 as 'success' but we need to explicitly handle them