Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Changes * to + to be more precise with acceptable branch names

We repeat the same code in many places. With the support of multiple
extends, we can clean up several jobs.

Note: This commit relies on
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26801
which brings support to multiple extends.

While `cache: {}` can disable a cache being set globally, it doesn't
work with extends, which will perform a reverse deep merge based on the
keys.

The cache defined in the base `.default-cache` job
won't be disabled in the report jobs.

As a side effect, the `code_quality`, `sast`, and `dependency_scanning`
jobs are running on a larger code base than expected, leading to
timeouts.

fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/11303
fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/60879
fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/12021

This updates our build images to use node@12. We are also adding a
sentence to the from-source installation that while we require a minimum
version of node@8, we also recommend node@12. Last but not least, we
change the version of node in the .nvmrc so that developers using nvm
can automatically use node@12 with the project

This commit adds CI job that validates all `*.yml`
with `yamllint`.

This commit fixes all offenses present in repository.

Ruby 2.6 offers better performance and memory usage:
https://www.rubyguides.com/2018/11/ruby-2-6-new-features/

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/57323

Signed-off-by: Rémy Coutable <remy@rymai.me>