Instrument `RepositoryCheck::SingleRepositoryWorker` manually

See merge request !4446

This worker is called manually by `RepositoryCheck::BatchWorker` meaning it's not tracked automatically by the Sidekiq middleware.

Add new GitLab CI configuration facade class

## What does this MR do?

This MR is a first iteration of major CI configuration refactoring. See #17139 and #15060 for more details.

## What are the relevant issue numbers?

Closes #17139

See merge request !4462

Ability to prioritize labels

Closes #14189 

See merge request !4009

Fix knapsack for master

It were mistakenly to invoke `rspec` where it should invoke `spinach`.


See merge request !4510

Use Knapsack to evenly distribute specs

Try to distribute all tests evenly accross all nodes to reduce the testing time of GitLab CE.

This uses high amount of auto-scaled machines.


See merge request !4240

Added 8.9 install/update guides

See merge request !4507

[ci skip]

Workhorse to serve raw diffs

Fixes (partially) #13999

Dependent on: gitlab-org/gitlab-workhorse!45

See merge request !4130

Rename ci_commit in application code

This is third iteration of renaming `[ci_]commit(s)` in application code to `pipeline(s)`.


See merge request !4464

Rename Ci::Commit in specs

This is second iteration of renaming Ci::Commit occurences, this time I try to rename all `let's` and `factories` to match what type of object is created:

1. Rename factories: `ci_[...]_commit_[...]` to `ci_[...]_pipeline_[...]`,
2. Rename all `let's(:[ci_]commit)` to `let(:pipeline)`,
3. Rename all occurrences of `[ci_]commit` to `pipeline` if Pipeline object is created

cc @grzesiek @DouweM 

See merge request !4463

# Conflicts:
#	.gitlab-ci.yml

This is a temporary refactoring stub, that is planned to be removed
after removing legacy config processor.

License finder gem

Every time a gem is added to the Gemfile, or a gem is updated with a new dependency or change of license, LicenseFinder will check to ensure that the license in use has been whitelisted for use in the project. GPLv2 and GPLv3 libraries are not allowed to be linked-to from non-GPL projects (e.g. the MIT-licensed GitLab CE or proprietary EE), otherwise we're violating the license.

https://github.com/pivotal/LicenseFinder

See also: gitlab-com/operations#164

See merge request !3775

Fix missed colorize methods.

Fix #18250.

cc: @twk3 

See merge request !4495

Bump rouge to 1.11.0

See: https://github.com/jneen/rouge/blob/master/CHANGELOG.md

See merge request !4491

Use better_errors editor links in sherlock

Closes #18254. Uses the same editor configuration of `better_errors`
so that you don't have to configure things twice. Remember to have a
custom initializer that specifies your editor.

Example for atom. File `config/initializers/better_errors.rb`:
````ruby
if defined?(BetterErrors)
  BetterErrors.editor = "atm://open?url=file://%{file}&line=%{line}"
end
````

See merge request !4497

Remember to configure your `better_errors` editor to point to your program of preference