Stub retryable http values in tests

See merge request https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/708

Merged-by: Ash McKenzie <amckenzie@gitlab.com>
Approved-by: Oscar Tovar <otovar@gitlab.com>
Approved-by: Ash McKenzie <amckenzie@gitlab.com>
Reviewed-by: Oscar Tovar <otovar@gitlab.com>
Co-authored-by: Igor Drozdov <idrozdov@gitlab.com>

Specify CGO_CFLAGS in Makefile to compile gssapi lib

See merge request https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/709

Merged-by: Stan Hu <stanhu@gmail.com>
Co-authored-by: Igor Drozdov <idrozdov@gitlab.com>

Currently, the default values are used for retryable http.
That's why a test waits 1 second minimun to retry a request.
Client test takes 25 seconds to execute as a result.
When we stub the value to 1 millisecond instead, we get 0.5s of
execution

Add support for the gssapi-with-mic auth method

Closes #196

See merge request https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/682

Merged-by: Igor Drozdov <idrozdov@gitlab.com>
Approved-by: Alejandro Rodríguez <alejandro@gitlab.com>
Approved-by: Patrick Bajao <ebajao@gitlab.com>
Approved-by: Costel Maxim <cmaxim@gitlab.com>
Approved-by: Igor Drozdov <idrozdov@gitlab.com>
Reviewed-by: Alejandro Rodríguez <alejandro@gitlab.com>
Reviewed-by: Igor Drozdov <idrozdov@gitlab.com>
Reviewed-by: Patrick Bajao <ebajao@gitlab.com>
Reviewed-by: Rohit Shambhuni <rshambhuni@gitlab.com>
Co-authored-by: Lee Tickett <ltickett@gitlab.com>
Co-authored-by: Marin Hannache <git@mareo.fr>

docs: Truncate pages, point users to GitLab repo

See merge request https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/705

Merged-by: Igor Drozdov <idrozdov@gitlab.com>
Approved-by: Torsten Linz <tlinz@gitlab.com>
Approved-by: Jerry Seto <jseto@gitlab.com>
Approved-by: Sean Carroll <scarroll@gitlab.com>
Approved-by: Igor Drozdov <idrozdov@gitlab.com>
Co-authored-by: Amy Qualls <aqualls@gitlab.com>

Release 14.15.0 version

See merge request https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/707

Merged-by: Igor Drozdov <idrozdov@gitlab.com>
Approved-by: Igor Drozdov <idrozdov@gitlab.com>