Merge branch '2736-cng-ci-ubi-release-for-certification-job-is-not-pulling-ubi-images' into 'master'

Adding -ubi8 to version to find UBI images

Closes gitlab-org/charts/gitlab#2736

See merge request gitlab-org/build/CNG!678

fix: correct error message for both backup and restore procedure

See merge request gitlab-org/build/CNG!631

Update Go to v1.16.4

See merge request gitlab-org/build/CNG!691

Release notes:
https://golang.org/doc/devel/release#go1.16.minor

This mirrors the change in Omnibus:

* https://gitlab.com/gitlab-org/gitlab-omnibus-builder/-/merge_requests/177
* https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/5374

Changelog: changed

Update our kubectl version to 1.16

See merge request gitlab-org/build/CNG!688

This updates our min-supported version to 1.15

Bump Container Registry to v3.5.0-gitlab

See merge request gitlab-org/build/CNG!687

gitlab-ruby: bump bundler version

See merge request gitlab-org/build/CNG!685

See https://gitlab.com/gitlab-org/build/CNG/-/merge_requests/685#note_592490911

Remove reference to experimental queue selector

See merge request gitlab-org/build/CNG!679

Missing s3cmd options when listing existing backups

See merge request gitlab-org/build/CNG!681

Bump gitlab-exporter to 10.3.0

See merge request gitlab-org/build/CNG!682

Add PROXY support to gitlab-shell container

See merge request gitlab-org/build/CNG!657

Bump Bundler version to latest as of 2020-06-02

Set the default user to `git`

This commit adds a new container, `gitlab-shell-libproxyproto`, that
supports the PROXY protocol
(https://developers.cloudflare.com/spectrum/proxy-protocol) via
libproxyproto (https://github.com/msantos/libproxyproto). This allows
the SSH server to get the real client IP instead of the IP of the load
balancer.

By default, the PROXY protocol is not enforced. This can be enabled in
the Helm Chart via this config:

```yaml
gitlab:
  gitlab-shell:
    enabled: true
    extraEnv:
      LIBPROXYPROTO_MUST_USE_PROTOCOL_HEADER: 1
```

Debugging can be enabled via `LIBPROXYPROTO_DEBUG: 1`.

Relates to https://gitlab.com/groups/gitlab-com/gl-infra/-/epics/425

Use only sidekiq cluster

See merge request gitlab-org/build/CNG!680

This updates the Puma dependency to 5.3.2

And remove support for running without cluster

remove references to Unicorn for 14.0 release

See merge request gitlab-org/build/CNG!665

Allow ubi-release-for-certification job to fail

See merge request gitlab-org/build/CNG!676

Update to UBI 8.4

Closes gitlab-org/charts/gitlab#2740

See merge request gitlab-org/build/CNG!677

Fix registry healthcheck

See merge request gitlab-org/build/CNG!675

And also add it for the non-ubi images

gitlab-rails: checks/postgresql detect silent NoDatabaseError

See merge request gitlab-org/build/CNG!663

Pin versions of perl and perl-libnetcfg in UBI

See merge request gitlab-org/build/CNG!673