As of part 5 on feature freeze day, we update the license list

https://gitlab.com/gitlab-org/release/docs/blob/7a3b6468aed8b254a26c202e98d8476ec3d6c046/general/release-candidates.md#step-5-update-the-dependencies-license-list-on-gitlab-ce

As part of step 4 on feature freeze day, we need to update the
templates.

https://gitlab.com/gitlab-org/release/docs/blob/7a3b6468aed8b254a26c202e98d8476ec3d6c046/general/release-candidates.md#step-4-update-the-gitignore-and-dockerfile-templates-on-gitlab-ce

Upgrade Prometheus to 2.4.3 and Alertmanager to 0.15.2

This saves about 128 MB of baseline RAM usage per Unicorn and
Sidekiq process (!).

Linguist wasn't detecting languages anymore from CE/EE since
9ae8b574. However, Linguist::BlobHelper
was still being depended on by BlobLike and others.

This removes the Linguist gem, given it isn't required anymore.
EscapeUtils were pulled in as dependency, but given Banzai depends on
it, it is now added explicitly.

Previously, Linguist was used to detect the best ACE mode. Instead,
we rely on ACE to guess the best mode based on the file extension.

Cleanup code, and refactor tests that still use Rugged. After this, there should
be no Rugged code that access the instance's repositories on non-test
environments. There is still some rugged code for other tasks like the
repository import task, but since it doesn't access any repository storage path
it can stay.

Uses curl instead of wget on install_dependencies, as wget does not
support https through http proxy on alpine:latest

Vendors in Auto-DevOps.gitlab-ci.yml from
https://gitlab.com/gitlab-org/gitlab-ci-yml/merge_requests/195

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/50186

Vendor Auto-DevOps.gitlab-ci.yml from https://gitlab.com/gitlab-org/gitlab-ci-yml/merge_requests/193

Thanks @LaurentGoderre, for your contribution !

vendored from https://gitlab.com/gitlab-org/gitlab-ci-yml/merge_requests/188

vendored from https://gitlab.com/gitlab-org/gitlab-ci-yml/merge_requests/186

Thanks @sgerrand !

Vendored in from https://gitlab.com/gitlab-org/gitlab-ci-yml/merge_requests/185

Thanks @sgerrand

See https://gitlab.com/gitlab-org/gitlab-ci-yml/merge_requests/184

Thanks to @kinolaev for this contribution.