Add latest changes from gitlab-org/gitlab@master

.gitattributes

.gitlab-ci.yml

.gitlab/ci/ee-specific-checks.gitlab-ci.yml

.gitlab/ci/rails.gitlab-ci.yml

.gitlab/ci/test-metadata.gitlab-ci.yml

.gitlab/issue_templates/Feature proposal.md

.license_encryption_key.pub

.rubocop.yml

CHANGELOG-EE.md

CHANGELOG.md

CONTRIBUTING.md

Gemfile

Gemfile.lock

app/assets/javascripts/boards/models/list.js

app/assets/javascripts/clusters/clusters_bundle.js

app/assets/javascripts/clusters/services/clusters_service.js

app/assets/javascripts/clusters/stores/clusters_store.js

app/assets/javascripts/gl_dropdown.js

app/assets/javascripts/gl_dropdown/render.js

app/assets/javascripts/groups/transfer_dropdown.js